Container for radioactive waste

ABSTRACT

A method of forming a sealed canister and a method of storing radioactive materials is provided. The method of forming includes placing a top plate on a top opening of a side wall, a bottom of the side wall being sealed to a base plate. The top plate includes a top surface with a top edge having a bevel and with a channel set in from the top edge. Finally, a weld is formed between the beveled top edge and the top opening of the side wall to seal the top plate to the side wall.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 14/358,032, filed May 13, 2014, which is a U.S.national stage application under 35 U.S.C. § 371 of PCT Application No.PCT/US2012/065117, filed Nov. 14, 2012, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/559,251, filed Nov. 14, 2011.

The present application is also a continuation-in-part of U.S. patentapplication Ser. No. 15/370,877, filed Dec. 6, 2016, which is acontinuation of U.S. patent application Ser. No. 15/053,608, filed Feb.25, 2016, now U.S. Pat. No. 9,514,853.

U.S. patent application Ser. No. 15/053,608 is a continuation-in-part ofU.S. patent application Ser. No. 14/534,391, filed Nov. 6, 2014, nowU.S. Pat. No. 9,293,229, which is a continuation of U.S. patentapplication Ser. No. 13/208,915, filed Aug. 12, 2011, now U.S. Pat. No.8,905,259, which in turn claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/373,138, filed Aug. 12, 2010.

U.S. patent application Ser. No. 15/053,608 is also acontinuation-in-part of U.S. patent application Ser. No. 14/394,233,filed Oct. 13, 2014, now U.S. Pat. No. 9,396,824, which is a U.S.national stage application under 35 U.S.C. § 371 of PCT Application No.PCT/US2013/036592, filed on Apr. 15, 2013, which claims the benefit ofU.S. Provisional Patent Application No. 61/624,066 filed Apr. 13, 2012.

U.S. patent application Ser. No. 15/053,608 is also acontinuation-in-part of U.S. patent application Ser. No. 14/395,790,filed Oct. 20, 2014, now U.S. Pat. No. 9,831,005, which is a U.S.national stage application under 35 U.S.C. § 371 of PCT Application No.PCT/US2013/037228, filed on Apr. 18, 2013, which claims the benefit ofU.S. Provisional patent application 61/625,869, filed Apr. 18, 2012.

U.S. patent application Ser. No. 15/053,608 is also acontinuation-in-part of U.S. patent application Ser. No. 14/424,201,filed Feb. 26, 2015, now U.S. Pat. No. 9,442,037, which is a U.S.national stage application under 35 U.S.C. § 371 of PCT Application No.PCT/US2013/057855, filed Sep. 31, 2013, which claims priority to U.S.Provisional Application Ser. No. 61/695,837, filed Aug. 31, 2012.

U.S. patent application Ser. No. 15/053,608 is also acontinuation-in-part of U.S. patent application Ser. No. 14/655,860,filed Jun. 25, 2015, now U.S. Pat. No. 9,779,843, which is a U.S.national stage application under 35 U.S.C. § 371 of PCT Application No.PCT/US2013/077852 filed Dec. 26, 2013, which claims priority to U.S.Provisional Application Ser. No. 61/746,094 filed Dec. 26, 2012.

U.S. patent application Ser. No. 15/053,608 is also acontinuation-in-part of U.S. patent application Ser. No. 14/762,874,filed Jul. 23, 2015, now U.S. Pat. No. 9,466,400, which is a U.S.national stage application under 35 U.S.C. § 371 of PCT Application No.PCT/US2014/013185, filed Jan. 27, 2014, which claims priority to U.S.provisional application No. 61/756,787, filed Jan. 25, 2013, and to U.S.provisional application No. 61/902,559, filed Nov. 11, 2013.

The disclosures of the aforementioned priority applications areincorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

The storage, handling, and transfer of high level waste, (hereinafter,“HLW”) such as spent nuclear fuel (hereinafter, “SNF”), requires specialcare and procedural safeguards. For example, in the operation of nuclearreactors, it is customary to remove fuel assemblies after their energyhas been depleted down to a predetermined level. Upon removal, thisspent nuclear fuel is still highly radioactive and produces considerableheat, requiring that great care be taken in its packaging, transporting,and storing. In order to protect the environment from radiationexposure, spent nuclear fuel is first placed in a canister. The loadedcanister is then transported and stored in large cylindrical containerscalled casks. A transfer cask is used to transport spent nuclear fuelfrom location to location while a storage cask is used to store spentnuclear fuel for a determined period of time.

In a typical nuclear power plant, an open empty canister is first placedin an open transfer cask. The transfer cask and empty canister are thensubmerged in a pool of water. Spent nuclear fuel is loaded into thecanister while the canister and transfer cask remain submerged in thepool of water. Once fully loaded with spent nuclear fuel, a lid istypically placed atop the canister while in the pool. The transfer caskand canister are then removed from the pool of water, the lid of thecanister is welded thereon and a lid is installed on the transfer cask.The canister is then properly dewatered and filled with inert gas. Thetransfer cask (which is holding the loaded canister) is then transportedto a location where a storage cask is located. The loaded canister isthen transferred from the transfer cask to the storage cask for longterm storage. During transfer from the transfer cask to the storagecask, it is imperative that the loaded canister is not exposed to theenvironment.

One type of storage cask is a ventilated vertical overpack (“VVO”). AVVO is a massive structure made principally from steel and concrete andis used to store a canister loaded with spent nuclear fuel (or otherHLW). VVOs stand above ground and are typically cylindrical in shape andextremely heavy, weighing over 150 tons and often having a heightgreater than 16 feet. VVOs typically have a flat bottom, a cylindricalbody having a cavity to receive a canister of spent nuclear fuel, and aremovable top lid.

In using a VVO to store spent nuclear fuel, a canister loaded with spentnuclear fuel is placed in the cavity of the cylindrical body of the VVO.Because the spent nuclear fuel is still producing a considerable amountof heat when it is placed in the VVO for storage, it is necessary thatthis heat energy have a means to escape from the VVO cavity. This heatenergy is removed from the outside surface of the canister byventilating the VVO cavity. In ventilating the VVO cavity, cool airenters the VVO chamber through bottom ventilation ducts, flows upwardpast the loaded canister, and exits the VVO at an elevated temperaturethrough top ventilation ducts. The bottom and top ventilation ducts ofexisting VVOs are located near the bottom and top of the VVO'scylindrical body respectively.

While it is necessary that the VVO cavity be vented so that heat canescape from the canister, it is also imperative that the VVO provideadequate radiation shielding and that the spent nuclear fuel not bedirectly exposed to the external environment. The inlet duct locatednear the bottom of the overpack is a particularly vulnerable source ofradiation exposure to security and surveillance personnel who, in orderto monitor the loaded overpacks, must place themselves in close vicinityof the ducts for short durations. Thus, a need exists for a VVO systemfor the storage of high level radioactive waste that has an inlet ductthat reduces the likelihood of radiation exposure while providingextreme radiation blockage of both gamma and neutron radiation emanatingfrom the high level radioactive waste.

The effect of wind on the thermal performance of a ventilated system canalso be a serious drawback that, to some extent, afflicts all systems inuse in the industry at the present time. Storage VVO' s with only twoinlet or outlet ducts are especially vulnerable. While axisymmetric airinlet and outlet ducts behave extremely well in quiescent air, when thewind is blowing, the flow of air entering and leaving the system isskewed, frequently leading to a reduced heat rejection capacity.

The thick top lid is one of the most expensive components of aradioactive waste canister. Such canisters may be used to store andtransport non-fuel radioactive waste from nuclear generation plants suchas activated reactor internals, control components, sundry non-fissilematerials, and waste from operations such as resins, and in someapplications vitrified nuclear waste fuel (“glass logs”) encased in anouter metal cylinder. On existing canisters, the thick top lid is neededto shield personnel from radiation who are working on the lid (e.g.welding, bolting, fluid operations, etc.). The lid must also be thickerbecause the lid further performs the main canister lifting connection,and therefore must have the thickness needed for structural reasons tosupport the weight of the entire canister when hoisted via a crane orsimilar equipment used to move the canister. For these reasons, thethick top lid of a waste canister adds considerably to the overallweight and expense of the canister. An improved radioactive wastecanister is desired.

A need also exists periodic leak testing is often required formonitoring the integrity of the inner and outer confinement boundarieson canisters holding radioactive materials. Some present leak testingprocesses involve removing the cask lid, which is undesirable, as doingso has the potential to increase radiation exposure to workers. Otherleak testing processes and systems involve installing a continuous leaktesting monitoring system that uses a compressed helium tank andpressure transducers. Such a system, however, requires periodicreplacement of the transducers and replenishment of the helium gasstored in the tank. In view of the shortcomings of present leakdetection processes and systems, improvements are desirable which reducethe on-site maintenance requirements, improve leak detectioncapabilities, and reduce potential radiation exposure to workers.

A need also exists for the ability to better examine welds formed oncontainers that are used to store spend nuclear fuel. Finally, a needexists to better enable spent nuclear fuel to be transferred from placeto place as necessary.

BRIEF SUMMARY OF THE INVENTION

These, and other drawbacks, are remedied by the present invention.

In one embodiment, the invention can be a system for storing high levelradioactive waste comprising: an overpack body extending along avertical axis and having a cavity for storing high level radioactivewaste, the cavity having an open top end and a floor; an overpack lidpositioned atop the overpack body to enclose the open top end of thecavity; an air inlet vent for introducing cool air into the cavity, theair inlet vent extending from an opening in an outer surface of theoverpack body to an opening in the floor, the opening in the outersurface of the overpack body extending about an entirety of acircumference of the outer surface of the overpack body; and an airoutlet vent in the overpack lid for removing warmed air from the cavity.

In another embodiment, the invention can be a system for storing highlevel radioactive waste comprising: an overpack body extending along avertical axis and having a cavity for storing high level radioactivewaste, the cavity having an open top end and a floor, the overpack bodycomprising an air inlet vent for introducing cool air into a bottomportion of the cavity; a plurality of plates disposed within a portionof the air inlet vent, each of the plates extending along a referenceline that is tangent to a third reference circle having a center pointcoincident with the vertical axis; and an overpack lid positioned atopthe overpack body to enclose the open top end of the cavity, theoverpack lid comprising an air outlet vent for removing warmed air fromthe cavity.

In yet another embodiment, the invention can be a system for storinghigh level radioactive waste comprising: an overpack body extendingalong a vertical axis and having a cavity for storing high levelradioactive waste, the cavity having an open top end and a floor, theoverpack body comprising an air inlet vent for introducing cool air intoa bottom portion of the cavity; an overpack lid positioned atop theoverpack body to enclose the open top end of the cavity, the overpacklid comprising an air outlet vent for removing warmed air from a topportion of the cavity; and the air inlet vent comprising a first sectionthat extends substantially horizontally from an outer surface of theoverpack body to a terminal end and a second section extending from thefirst section of the air inlet vent to an opening in the floor at anoblique angle relative to the vertical axis.

In still another embodiment, the invention can be a radioactive wastecontainer system comprising: a canister having an interior chamber forholding radioactive waste and an open top; a lid assembly comprising aconfinement lid and a shielded lifting lid, the confinement lid beingdetachably mounted to the lifting lid; the confinement lid beingconfigured for mounting on the canister and having a first thickness;the lifting lid including a lifting attachment and having a secondthickness; wherein the confinement lid is independently mountable oncanister from the lifting lid.

In still a further embodiment, the invention can be a radioactive wastecontainer system comprising: a canister having an interior chamber forholding radioactive waste and an open top; a lid assembly comprising alower confinement lid and an upper shielded lifting lid, the confinementlid being detachably bolted to the lifting lid; the lifting lidincluding a plurality of first bolt holes having a first diameter and aplurality of second bolt holes having a second diameter, the firstdiameter being larger than the second diameter; the confinement lidincluding a plurality of third bolt holes having a third diameter,wherein each of the third bolt holes is concentrically aligned with oneof the first or second bolt holes of the lifting lid; and a plurality offirst mounting bolts inserted through the first bolt holes andthreadably attaching the confinement lid to the canister withoutengaging the lifting lid.

In a yet further embodiment, the invention can be a method for storingradioactive waste using a container system, the method comprising:detachably mounting a confinement lid to a shielded lifting lid, theconfinement lid and shielded lifting lid collectively forming a lidassembly; placing a canister having an interior chamber for holdingradioactive waste into an outer protective overpack; lifting the lidassembly using the lifting lid; placing the lid assembly on an open topof the canister; attaching the confinement lid to the canister using afirst set of mounting bolts without threadably engaging the lifting lidwith the bolts; detaching the lifting lid from the confinement lid; andremoving the lifting lid from the canister.

In another embodiment, the invention can be a module for storing highlevel radioactive waste, the module comprising: an outer shell having ahermetically closed bottom end; an inner shell forming a cavity, theinner shell positioned inside the outer shell so as to form a spacebetween the inner shell and the outer shell; at least one dividerextending from a top of the inner shell to a bottom of the inner shell,the at least one divider creating a plurality of inlet passagewaysthrough the space, each inlet passageway connecting to a bottom portionof the cavity; a plurality of inlet ducts, each inlet duct connecting atleast one of the inlet passageways to ambient atmosphere and eachcomprising an inlet duct cover affixed over a surrounding inlet wall,the inlet wall being peripherally perforated; and a removable lidpositioned atop the inner shell, the lid having at least one outletpassageway connecting the cavity and the ambient atmosphere, wherein thelid and a top of the inner shell are respectively configured to form ahermetic seal at a top of the cavity.

In still another embodiment, the invention can be a system for storingradioactive materials, the system comprising: a canister comprising: afirst hermetically sealed vessel having a first cavity; a secondhermetically sealed vessel having a second cavity, wherein the firstvessel is positioned in the second cavity; an interstitial space betweenthe first and second vessels; and a test port through the second vesselin fluidic communication with the interstitial space; a conduit having afirst end fluidically coupled to the test port; and a removable sealoperably coupled to a second end of the conduit.

In yet another embodiment, the invention can be a method of storingradioactive materials, the method comprising: a) providing a cask havinga cask body that forms a cask cavity having an open top end; b)positioning a canister loaded with the radioactive materials in the caskcavity, the canister comprising a first hermetically sealed vesselhaving a first cavity in which the radioactive materials are disposedand a second hermetically sealed vessel having a second cavity, whereinthe first vessel is positioned in the second cavity, such that aninterstitial space exists between the first and second vessels, andwherein the second vessel includes a test port that is in fluidiccommunication with the interstitial space; c) fluidically coupling afirst end of a conduit to the test port, the conduit extending from thefirst end to a second end located outside of the cask; and d) securing acask lid to the cask body to substantially enclose the open top end ofthe cask cavity.

In another embodiment still, the invention can be a system for leaktesting a canister containing radioactive materials, the systemcomprising: a canister comprising: a first hermetically sealed vesselhaving a first cavity; a second hermetically sealed vessel having asecond cavity, wherein the first vessel is positioned in the secondcavity; an interstitial space between the first and second vessels; anda test port through the second vessel in fluidic communication with theinterstitial space; a conduit having a first end fluidically coupled tothe test port; a removable seal operably coupled to a second end of theconduit; and a leak detector configured to operably couple to the secondend of the conduit and to detect whether a leak exists in at least oneof the first vessel and the second vessel.

In a further embodiment, the invention can be a method of leak testing astorage canister for radioactive materials, the method comprising: a)positioning the canister in a cask cavity of a cask body, the canistercomprising a first hermetically sealed vessel having a first cavity inwhich the radioactive materials are disposed and a second hermeticallysealed vessel having a second cavity, the first vessel positioned in thesecond cavity such that an interstitial space exists between the firstand second vessels, and wherein the second vessel includes a test portthat is in fluidic communication with the interstitial space; b)coupling a first end of a conduit to the test port, the conduitextending from the first end to a second end located outside of the caskbody; c) securing a cask lid to the cask body to substantially enclosethe cask cavity; and d) operatively coupling a leak detector to thesecond end of the conduit to perform a leak test comprising determiningwhether a leak exists in at least one of the first vessel and the secondvessel

In a still further embodiment, the invention can be a method of leaktesting a canister containing radioactive materials, the methodcomprising: a) coupling a first end of a conduit to a test port of thecanister that is in fluid communication with an interstitial space ofthe canister, the conduit extending from the first end to a second end;and b) operatively coupling a leak detector to the second end; c)drawing gas from the conduit using the leak detector to establish avacuum within the conduit and the interstitial space; and d) monitoringthe drawn gas for the presence of a first indicator which isrepresentative of a leak in a fluidic containment boundary of thecanister that contains the radioactive materials.

In another embodiment, the invention can be a canister for storingradioactive materials, the canister comprising: a base plate; a sidewall having a bottom sealed to the base plate; and a top plate includinga top surface with a top edge having a bevel and with a channel set infrom the top edge, wherein a weld is formed between the beveled top edgeand a top of the side wall to seal the top plate to the side wall, andwherein the base plate, side wall, and top plate form a sealed vessel.

In another embodiment, the invention can be a method of forming a sealedcanister, the method comprising: placing a top plate on a top opening ofa side wall, a bottom of the side wall being sealed to a base plate,wherein the top plate includes a top surface with a top edge having abevel and with a channel set in from the top edge; and forming a weldbetween the beveled top edge and the top opening of the side wall toseal the top plate to the side wall.

In another embodiment, still, the invention can be a method of storingradioactive materials, the method comprising: placing radioactivematerials in a cavity formed by a side wall having a bottom sealed to abase plate; placing a top plate on a top opening of the side wall, thetop plate including a top surface with a top edge having a bevel andwith a channel set in from the top edge; forming a weld between thebeveled top edge and the top opening of the side wall to seal the topplate to the side wall, so that the cavity is sealed; placing a firstprobe in the channel and a second probe opposite the first probe andadjacent the side wall, such that the weld is disposed between the twoprobes; activating the first and second probes to determine an integrityof a volume of the weld between the probes; and moving the first andsecond probes synchronously around the top plate to determine theintegrity of an entire volume of the weld.

In another embodiment, the invention can be an apparatus fortransferring spent nuclear fuel, the apparatus comprising: a cylindricalinner shell forming a cavity configured to receive a canister containingspent nuclear fuel, the cavity configured so that an annulus is formedbetween a canister placed in the cavity and an inner wall of thecylindrical inner shell; an intermediate shell disposed concentricallyaround and spaced apart from the inner shell; an outer shell disposedconcentrically around and spaced apart from the intermediate shell; abottom flange affixed to bottoms of each of the shells; a bottom lidremovably affixed to the bottom flange and including at least one firstchannel fluidically connecting the annulus to an exterior of the bottomlid, wherein the at least one first channel is configured to preclude adirect line of travel from within the cavity to the exterior of thebottom lid; a top flange affixed to tops of each of the shells andincluding at least one second channel fluidically connecting the firstannulus to an exterior of the top flange, wherein the at least onesecond channel is configured to preclude a direct line of travel fromwithin the cavity to the exterior of the top flange; and a top lidremovably affixed to the top flange.

In yet another embodiment, the invention can be an apparatus fortransferring spent nuclear fuel, the apparatus comprising: a cylindricalinner shell forming a cavity configured to receive a canister containingspent nuclear fuel; an intermediate shell disposed concentrically aroundand spaced apart from the inner shell; an outer shell disposedconcentrically around and spaced apart from the intermediate shell; abottom flange affixed to bottoms of each of the shells; a bottom lidremovably affixed to the bottom flange; a top flange affixed to tops ofeach of the shells, the top flange including at least two integrallyformed trunnions configured to enable hoisting of the apparatus; and atop lid removably affixed to the top flange.

In still another embodiment, the invention can be an apparatus fortransferring spent nuclear fuel, the apparatus comprising: a cylindricalinner shell forming a cavity configured to receive a canister containingspent nuclear fuel; an intermediate shell disposed concentrically aroundand spaced apart from the inner shell; an outer shell disposedconcentrically around and spaced apart from the intermediate shell; abottom flange affixed to bottoms of each of the shells; a bottom lidremovably affixed to the bottom flange, the bottom lid including animpact zone comprising an impact absorbing structure; a top flangeaffixed to tops of each of the shells; and a top lid removably affixedto the top flange.

In another embodiment, the invention can be a method for transferringspent nuclear fuel from a pool, the method comprising: lifting atransfer cask from a pool, the transfer cask comprising: a cylindricalinner shell forming a cavity configured to receive a canister containingspent nuclear fuel, the cavity configured so that an annulus is formedbetween a canister placed in the cavity and an inner wall of thecylindrical inner shell; an intermediate shell disposed concentricallyaround and spaced apart from the inner shell; an outer shell disposedconcentrically around and spaced apart from the intermediate shell; abottom flange affixed to bottoms of each of the shells; a bottom lidremovably affixed to the bottom flange and including at least one firstchannel fluidically connecting the annulus to a channel inlet at anexterior of the bottom lid, wherein the at least one first channel isconfigured to preclude a direct line of travel from within the cavity tothe exterior of the bottom lid; a removable plug sealingly affixed tothe channel inlet; a top flange affixed to tops of each of the shellsand including at least one second channel fluidically connecting thefirst annulus to an exterior of the top flange, wherein the at least onesecond channel is configured to preclude a direct line of travel fromwithin the cavity to the exterior of the top flange; and a top lidremovably affixed to the top flange; removing the removable plug fromthe channel inlet, thereby allowing ambient air to enter the at leastone first channel; draining the pool water from the canister; and movingthe transfer cask to a staging area.

In another embodiment, the invention can be a ventilated system forstoring high level radioactive waste comprising: a cask body comprisingan outer surface and an inner surface forming a storage cavity forreceiving high level radioactive waste; a cask lid positioned atop thecask body and enclosing a top end of the storage cavity; at least oneoutlet duct extending from a top of the storage cavity to an ambientatmosphere; a plurality of inlet ducts, each of the inlet ductsextending from a first opening in the outer surface of the cask body toa second opening in the inner surface of the cask body, the plurality ofinlet ducts comprising a lowermost set of inlet ducts and an uppermostset of inlet ducts; and wherein the second openings of the lowermost setof air inlet ducts are located at a first vertical distance from abottom end of the cask body and the second openings of the uppermost setof air inlet ducts are located at a second vertical distance from thebottom end of the cask body, the second vertical distance being greaterthan the first vertical distance.

In yet another embodiment, the invention can be a ventilated system forstoring high level radioactive waste comprising: a cask body comprisinga bottom end, a top end, an outer surface and an inner surface, theinner surface forming a storage cavity for receiving high levelradioactive waste, the cask body extending along a vertical axis fromthe bottom end to the top end and having a vertical height measured fromthe bottom end of the cask body to the top end of the cask body; a casklid positioned atop the cask body and enclosing a top end of the storagecavity; at least one outlet duct extending from a top of the storagecavity to an ambient atmosphere; a plurality of inlet ducts, each of theinlet ducts extending from a first opening in the outer surface of thecask body to a second opening in the inner surface of the cask body; thecask body comprising a lower axial section and an upper axial section,wherein the lower axial section is defined from the bottom end of thecask body to a vertical height of an uppermost one of the secondopenings of the plurality of air inlet ducts, and wherein the upperaxial section is defined from the top end of the cask body to thevertical height of the uppermost one of the second openings of theplurality air inlet ducts; a metal canister containing high levelradioactive waste positioned within the storage cavity so that anannular gap exists between an outer surface of the metal canister andthe inner surface of the cask body, the annular gap forming a passagewayfrom the second openings of the plurality of the inlet ducts to the atleast one outlet duct; the second openings of the plurality of air inletducts arranged in a pattern on the inner surface of the cask body alongthe lower axial section; and wherein the pattern is configured and thevertical height of the uppermost one of the second openings is selectedto maintain more than 90% of a vertical height of the metal canisterabove a predetermined threshold temperature for a predetermined heatgeneration rate of the high level radioactive waste.

In still another embodiment, the invention can be a method of storinghigh level radioactive waste comprising: a) positioning a metal canistercontaining high level radioactive waste having a heat generation rate ina storage cavity of a ventilated system comprising a cask body, a casklid positioned atop the cask body, at least one outlet duct extendingfrom a top of the storage cavity to an ambient atmosphere, and aplurality of inlet ducts, each of the inlet ducts extending from a firstopening in the outer surface of the cask body to a second opening in theinner surface of the cask body; and b) sealing selected ones of theplurality of inlet ducts over time as a function of a decay of the heatgeneration rate to maintain a predetermined percentage of a verticalheight of the metal canister above a predetermined threshold temperature

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is an isometric view of a vertical ventilated overpack inaccordance with an embodiment of the present invention;

FIG. 2 is a top view of the vertical ventilated overpack of FIG. 1;

FIG. 3 is a front view of the vertical ventilated overpack of FIG. 1;

FIG. 4 is a cross-sectional view of the vertical ventilated overpacktaken along line IV-IV of FIG. 2;

FIG. 5 is the cross-sectional view of the vertical ventilated overpackof FIG. 4 with a canister positioned within the cavity;

FIG. 6 is a cross-sectional view of the vertical ventilated overpacktaken along line VI-VI of FIG. 3;

FIG. 7 is a cross-sectional view of the vertical ventilated overpacktaken along line VII-VII of FIG. 3;

FIG. 8 is a close-up view of a portion of the vertical ventilatedoverpack illustrated in FIG. 4;

FIG. 9 is perspective view of a radioactive waste canister according toone embodiment of the present disclosure having a confinement lidmounted thereon;

FIG. 10 is a cross-sectional perspective view thereof with confinementlid removed and showing a waste cylinder basket insert;

FIG. 11 is a close-up view thereof of the top portion of the canistershowing details of the basket insert, a radiation containment barrier,and a bolting block;

FIG. 12 is a close-up view thereof of the bottom portion of the canistershowing details of the basket insert;

FIG. 13 is a perspective view of the canister of FIG. 9 disposed insidea protective overpack;

FIG. 14 is a perspective view thereof showing a plurality of wastecylinders installed in the basket insert of the canister;

FIG. 15 is a perspective view thereof also showing a coupled confinementlid-shielded lifting lid assembly being grappled and hoisted over theoverpack and canister;

FIG. 16 is a perspective view thereof showing the grappled confinementlid-shielded lifting lid assembly lowered and placed in position on theoverpack and canister;

FIG. 17 is a cross-sectional perspective view thereof of the upper leftcorner portion of the overpack and canister;

FIG. 18 is a top perspective view of the overpack showing theconfinement lid-shielded lifting lid positioned on the overpack;

FIG. 19 is a close-up perspective view thereof with a portion of theshielded lifting lid being shown cutaway to show details of theconfinement lid and shielded lifting lid bolting arrangement;

FIG. 20 is a perspective view thereof showing confinement lid mountingbolts in place;

FIG. 21 is a perspective view of the overpack lid;

FIG. 22 is a perspective view thereof showing the confinementlid-shielded lifting lid assembly and overpack of FIG. 16 with overpacklid alignment pins in place;

FIG. 23 is a perspective view of the grappled shielded lifting liduncoupled from the confinement lid and being removed from the overpackand canister, with the overpack lid staged for installation;

FIG. 24 is a perspective view of the grappled overpack lid lowered intoposition on the overpack;

FIG. 25 is a perspective view thereof with the overpack lid bolted ontothe overpack;

FIG. 26 is a perspective view of the fully assembled overpack;

FIG. 27A is a partially exploded perspective view of a HLW storagecontainer;

FIG. 27B is a top plan view of the HLW storage container of FIG. 27A;

FIG. 28 is a sectional view of the HLW storage container of FIG. 27Balong the line XXVIII-XXVIII;

FIG. 29 is a partial sectional view of the HLW storage container of FIG.27B along the line XXIX-XXIX;

FIG. 30A is a partial sectional view of the HLW storage container ofFIG. 27A;

FIG. 30B is a sectional view of the HLW storage container FIG. 30A alongthe line XXX-B-XXX-B;

FIG. 31A is a partial sectional view of the HLW storage container ofFIG. 27A having a canister positioned in the cavity;

FIGS. 31B-31D are detailed views of the indicated parts of FIG. 31A;

FIG. 32 is an isometric view of a lid for a HLW storage container;

FIG. 33 is a sectional view of the lid of FIG. 32;

FIG. 34 is a plan view of an array of HLW storage containers;

FIG. 35 is a top perspective view of a dual-walled DSC having a sectioncut-away;

FIG. 36 is an exploded view of the dual-walled DSC of FIG. 35 showingthe inner and outer top lids removed from the inner and outer shells;

FIG. 37 is a close-up view of the area XXXVII-XXXVII of FIG. 35;

FIG. 38 is a close-up view of the area XXXVIII-XXXVIII of FIG. 36;

FIG. 39A is a top view of a ventilated storage system;

FIG. 39B is a cross-sectional view of the ventilated storage system ofFIG. 39A along the line XXXIX-B;

FIG. 40 is a perspective view of a system for storing radioactivematerials;

FIG. 41 is a perspective view of an external enclosure for the system ofFIG. 40;

FIG. 42 is a perspective view of the external enclosure without thecover;

FIG. 43 is a detailed perspective view of a top portion of a ventilatedstorage system;

FIG. 44 is a detailed perspective view of a top portion of a ventilatedstorage system without the cask lid;

FIG. 45 is a partial cross-sectional view of a ventilated storage systemshowing the test port;

FIG. 46 is a partial cross-sectional view of two pressure vessels usedfor storing radioactive materials;

FIG. 47 is a schematic view of a radioactive waste storage system;

FIG. 48 illustrates the top lid welded to the side wall of a canisteraccording to the prior art;

FIG. 49A illustrates a double-walled MPC having lids configured to allow100% volumetric examination of the respective closure weld;

FIG. 49B illustrates a single walled MPC having a lid configured toallow 100% volumetric examination of the closure weld;

FIG. 49C illustrates a detailed sectional view of a lid and closureweld, the lid being configured to allow 100% volumetric examination ofthe closure weld;

FIG. 50 illustrates a top elevation view of a first lid configured toallow 100% volumetric examination of the closure weld;

FIG. 51 illustrates a top elevation view of a second lid configured toallow 100% volumetric examination of the closure weld;

FIG. 52A illustrates a weld arm positioned to form a closure weld andprobes positioned to volumetrically examine the closure weld;

FIG. 52B illustrates a detailed sectional view of a lid, the weld head,and the probes of FIG. 52A;

FIG. 53 is a cross-sectional view of a transfer cask;

FIG. 54A is a perspective view of a top flange for a transfer cask;

FIG. 54B is a schematic view of a first alternative trunnionconfiguration;

FIG. 54C is a schematic view of a second alternative trunnionconfiguration;

FIG. 55 is a perspective view of a bottom lid for a transfer cask;

FIG. 56 is a partial sectional view of a bottom portion of a firstalternative transfer cask;

FIG. 57 is a partial sectional view of a bottom portion of a secondalternative transfer cask;

FIG. 58 schematically shows a transfer tank coupled to a forced aircooling system;

FIG. 59 is a flow chart showing a process for moving a transfer caskloaded with a canister containing spent nuclear fuel out of a storagepool;

FIG. 60 is a perspective view of a prior art ventilated storage system;

FIG. 61 is a graph of air temperature as a function of distance from thebottom end of the cask body within the ventilated cask of the prior artventilated storage system of FIG. 60 when a canister loaded with highlevel radioactive waste having a heat load is positioned within theventilated cask;

FIG. 62 is a graph of the temperature of the outer surface of thecanister as a function of distance from the bottom end of the cask bodywhen the canister is stored in the ventilated cask of the prior artventilated storage system of FIG. 60;

FIG. 63 is a perspective view of a ventilated system according to anembodiment of the present invention;

FIG. 64 is a schematic cross-sectional view of the ventilated system ofFIG. 63;

FIG. 65 is perspective view of the cask body of the ventilated system ofFIG. 64 wherein a portion of the outer metal shell is cut-away and theconcrete fill has been removed from the annulus to reveal the inletducts; and

FIG. 66 is a comparative graph of the temperature of the outer surfaceof a canister as a function of distance from a bottom end of a cask bodywhen stored in the ventilated system of the present invention as opposedto being stored in the prior art ventilated cask of FIG. 60.

All drawings are schematic and not necessarily to scale. Parts given areference numerical designation in one figure may be considered to bethe same parts where they appear in other figures without a numericaldesignation for brevity unless specifically labeled with a differentpart number and described herein.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

The description of illustrative embodiments according to principles ofthe present invention is intended to be read in connection with theaccompanying drawings, which are to be considered part of the entirewritten description. In the description of embodiments of the inventiondisclosed herein, any reference to direction or orientation is merelyintended for convenience of description and is not intended in any wayto limit the scope of the present invention. Relative terms such as“lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,”“down,” “top,” and “bottom” as well as derivatives thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) should be construed torefer to the orientation as then described or as shown in the drawingunder discussion. These relative terms are for convenience ofdescription only and do not require that the apparatus be constructed oroperated in a particular orientation unless explicitly indicated assuch. Terms such as “attached,” “affixed,” “connected,” “coupled,”“interconnected,” and similar refer to a relationship wherein structuresare secured or attached to one another either directly or indirectlythrough intervening structures, as well as both movable or rigidattachments or relationships, unless expressly described otherwise.Moreover, the features and benefits of the invention are illustrated byreference to the exemplified embodiments. Accordingly, the inventionexpressly should not be limited to such exemplary embodimentsillustrating some possible non-limiting combination of features that mayexist alone or in other combinations of features; the scope of theinvention being defined by the claims appended hereto.

Multiple inventive concepts are described herein and are distinguishedfrom one another using headers in the description that follows.Specifically, FIGS. 1-8 are relevant to a first inventive concept, FIGS.9-26 are relevant to a second inventive concept, FIGS. 27-34 arerelevant to a third inventive concept, FIGS. 35-47 are relevant to afourth inventive concept, FIGS. 48-52B are relevant to a fifth inventiveconcept, FIGS. 53-59 are relevant to a sixth inventive concept, andFIGS. 60-66 are relevant to a seventh inventive concept. The firstthrough seventh inventive concepts should be considered in isolationfrom one another. It is possible that there may be conflicting languageor terms used in the description of the first through sixth inventiveconcepts. For example, it is possible that in the description of thefirst inventive concept a particular term may be used to have onemeaning or definition and that in the description of the secondinventive concept the same term may be used to have a different meaningor definition. In the event of such conflicting language, referenceshould be made to the disclosure of the relevant inventive concept beingdiscussed. Similarly, the section of the description describing aparticular inventive concept being claimed should be used to interpretclaim language when necessary.

I. Inventive Concept 1

With reference to FIGS. 1-8, a first inventive concept will bedescribed.

Referring to FIGS. 1-4 concurrently, a system for storing high levelradioactive waste will be described in accordance with an embodiment ofthe present invention. The system can be considered a VVO 100. The VVO100 is a vertical, ventilated dry spent fuel storage system that isfully compatible with 100 ton and 125 ton transfer casks for spent fuelcanister operations. Of course, the VVO 100 can be modified/designed tobe compatible with any size or style transfer cask. The VVO 100 isdesigned to accept spent fuel canisters for storage. All spent fuelcanister types engineered for storage in free-standing and anchoredoverpack models can be stored in VVO 100.

As used herein the term “canister” broadly includes any spent fuelcontainment apparatus, including, without limitation, multi-purposecanisters and thermally conductive casks. For example, in some areas ofthe world, spent fuel is transferred and stored in metal casks having ahoneycomb grid-work/basket built directly into the metal cask. Suchcasks and similar containment apparatus qualify as canisters, as thatterm is used herein, and can be used in conjunction with VVO 100 asdiscussed below.

In certain embodiments, the VVO 100 is a substantially cylindricalcontainment unit having a vertical axis A-A and a horizontalcross-sectional profile that is substantially circular in shape. Ofcourse, it should be understood that the invention is not limited tocylinders having circular horizontal cross sectional profiles but mayalso include containers having cross-sectional profiles that are, forexample, rectangular, ovoid or other polygon forms. While the VVO 100 isparticularly useful for use in conjunction with storing and/ortransporting SNF assemblies, the invention is in no way limited by thetype of waste to be stored. The VVO cask 100 can be used to transportand/or store almost any type of HLW. However, the VVO 100 isparticularly suited for the transport, storage and/or cooling ofradioactive materials that have a high residual heat load and thatproduce neutron and gamma radiation, such as SNF. This is because theVVO 100 is designed to both provide extreme radiation blockage of gammaand neutron radiation and facilitate a convective/no force cooling ofany canister contained therein.

The VVO 100 of the present invention generally comprises an overpackbody 110 for storing high level radioactive waste and a removableoverpack lid 120 that is positioned atop the overpack body 110. Theoverpack body 110 extends along the vertical axis A-A. The overpack lid120 generally comprises a primary lid 121 and a secondary lid 122. Theprimary lid 121 is secured to the overpack body 110 by bolts 123 thatrestrain separation of the primary lid 121 of the overpack lid 120 fromthe overpack body 110 in case of a tip over situation. Moreover, thesecondary lid 122 is secured to the primary lid 121 by bolts 124. Theoverpack lid 120 is a steel/concrete structure that is equipped with anaxisymmetric air outlet vent or passageway 145 for theventilation/removal of air as will be discussed in more detail below. Anannular opening 157 is formed in an outer sidewall surface 178 of theoverpack lid 120 that forms a passageway from the air outlet vent 145 tothe external environment. More specifically, the annular opening 157 isa 360° opening in the outer sidewall surface 178 of the overpack lid120. The overpack lid 120 has a quick connect/disconnect joint tominimize human activity for its installation or removal. In certainembodiments, the overpack lid 120 may weigh in excess of 15 tons.

The VVO 100 further comprises shock absorber or crush tubes 102 in itstop region. The shock absorber tubes 102 are arranged at suitableangular spacings to serve as a sacrificial crush material if, for anyreason, the VVO 100 were to tip over. The shock absorber tubes 102 alsofacilitate guiding and positioning of a canister within a cavity 111 ofthe VVO 100 in a substantially concentric disposition with respect tothe VVO 100.

Referring to FIGS. 1, 4 and 6 concurrently, the overpack body 110comprises a cylindrical wall 112, a bottom enclosure plate 130 and theoverpack lid 120 described above. The cylindrical wall 112 has an innershell 113, an intermediate shell 114 and an outer shell 115. In theexemplified embodiment, each of the inner, intermediate and outer shells113, 114, 115 are formed of one-inch thick steel. Of course, theinvention is not to be so limited and in other embodiments the inner,intermediate and outer shells 113, 114, 115 can be formed of metalsother than steel and can be greater or less than one-inch in thickness.The inner shell 113 has an inner surface 116 that defines an internalcavity 111 for containing a hermetically sealed canister that containshigh level radioactive waste (FIG. 5). The inner surface 116 of theinner shell 113 also forms the inner wall surface of the overpack body110. Furthermore, the outer shell 115 has an outer surface 117. Theouter surface 117 of the outer shell 115 also forms the outer sidewallsurface of the overpack body 110.

In the exemplified embodiment, the inner, intermediate and outer shells113, 114, 115 are concentric shells that are rendered into a monolithicweldment by a plurality of connector plates 105 a, 105 b. The innershell 113 is spaced from the intermediate shell 114 by connector plates105 a and the intermediate shell 114 is spaced from the outer shell 115by connector plates 105 b. Of course, in certain other embodiments theconnector plates 105 a, 105 b can be altogether omitted. The spacebetween the inner shell 113 and the intermediate shell 114 is intendedfor placement of a neutron shielding material. For example, in certainembodiments the neutron radiation shielding material is a hydrogen-richmaterial, such as, for example, Holtite, water or any other materialthat is rich in hydrogen and a Boron-10 isotope. In certain embodiments,there is approximately seven inches of Holtite filling the space betweenthe inner and intermediate shells 113, 114. Thus, the space between theinner and intermediate shells 113, 114 serves to prevent neutronradiation from passing through the VVO 100 and into the externalenvironment.

An axially intermediate portion of the space between the intermediateshell 114 and the outer shell 115 is filled with a heavy shieldingconcrete to capture and prevent the escape of both gamma and neutronradiation. The density of the concrete is preferably maximized toincrease the radiation absorption characteristics of the VVO 100. Incertain embodiments, there is approximately twenty-eight inches ofconcrete filling the intermediate portion of the space between theintermediate and outer shells 114, 115. In some embodiments, steelplates are placed within the concrete to serve as a supplementalradiation curtain. There are no lateral penetrations in the multi-shellweldment that may provide a streaming path for the radiation issuingfrom the high level radioactive waste.

The top and bottom portions of the space between the intermediate andouter shells 114, 115 (both above and below the concrete) are top andbottom forgings 128, 129 in the form of thick annular rings made of ametal material, such as steel. The top forging 128 comprises machinethreaded holes 126 that are sized and configured to receive the bolts123 of the primary lid 121 therein during attachment of the overpack lid120 to the overpack body 110.

As noted above, the inner surface 116 of the inner shell 113 defines thecavity 111. In the exemplified embodiment, the cavity 111 is cylindricalin shape. However, the cavity 111 is not particularly limited to anyspecific size, shape, and/or depth, and the cavity 111 can be designedto receive and store almost any shape of canister. In certainembodiments, the cavity 111 is sized and shaped so that it canaccommodate a canister of spent nuclear fuel or other HLW. Morespecifically, the cavity 111 has a horizontal cross-section that canaccommodate no more than one canister. Even more specifically, it isdesirable that the size and shape of the cavity 111 be designed so thatwhen a spent fuel canister is positioned in the cavity 111 for storage,a small clearance exists between outer side walls of the canister andthe inner surface 116 of the inner shell 113, as will be discussed inmore detail below with reference to FIG. 5.

Referring to FIGS. 4 and 5 concurrently, the present invention will befurther described. The cavity 111 comprises a floor 152 and an open topend 151 that is enclosed by the overpack lid 120 as has been describedherein above. A plurality of support blocks 153 are disposed on thefloor 152 of the cavity 111 to support a canister 200 contained withinthe cavity 111 above the floor 152. In the exemplified embodiment, foursupport blocks 153 are illustrated (see FIG. 6). However, more or lessthan four support blocks 153 can be used in alternate embodiments. Eachof the support blocks 153 is a low profile lug that is welded to theinner surface 116 of the inner shell 113 and/or to the floor 152. In theexemplified embodiment, the canister 200 is a hermetically sealedcanister for containing the high level radioactive waste. When thecanister 200 is positioned within the cavity 111, it rests atop thesupport blocks 153 so that a space 154 exists between a bottom 202 ofthe canister 200 and the floor 152. The space 154 is a bottom plenumthat serves as the recipient of ventilation air flowing up from an inletvent as will be described below.

Furthermore, when the canister 200 is positioned within the cavity 111,an annular gap 155 exists between the inner surface 116 of the innershell 113 (i.e., the inner wall surface of the overpack body 110) and anouter surface 201 of the canister 200. The annular gap 155 is anuninterrupted and continuous gap that circumferentially surrounds thecanister 200. In other words, the canister 200 is concentrically spacedapart from the inner shell 113, thereby creating the annular gap 155. Asdescribed in more detail below, the annular gap 155 forms an annular airflow passageway between an annular air inlet passageway 142 and the airoutlet vent 145.

The VVO 100 is configured to achieve a cyclical thermosiphon flow of gas(i.e., air) within the cavity 111 when spent nuclear fuel emanating heat(i.e., the canister 200) is contained therein. In other words, the VVO100 achieves a ventilated flow by virtue of a chimney effect. Suchcyclical thermosiphon flow of the gas further enhances the transmissionof heat to the environment external to the VVO 100. The thermosiphonflow of gas is achieved as a result of an air inlet vent 140 thatintroduces cool air into the bottom of the cavity 111 of the overpackbody 110 from the external environment and an air outlet vent 145 forremoving warmed air from the cavity 111. Thus, as a result ofthermosiphon flow, cool external air can enter into the space 154 of thecavity 111 between the bottom 202 of the canister 200 and the floor 152via the air inlet vent 140, flow upward through the cavity 111 withinthe annular gap 155 between the canister 200 and the inner surface 116of the inner shell 113, and flow back out into the external environmentas warmed air via the air outlet vent 145. The newly entered air willwarm due to proximity to the extremely hot canister 200, which willcause the natural thermosiphon flow process to take place whereby theheated air will continually flow upwardly as fresh cool air continues toenter into the cavity 111 via the air inlet vent 140. Thus, the airinlet vent 140 provides a passageway that facilitates cool air enteringthe cavity 111 from the external environment and the air outlet vent 145provides a passageway that facilitates warm air exiting the cavity backto the external environment.

In the exemplified embodiment, the air outlet vent 145 is formed intothe overpack lid 120. The air outlet vent 145 provides an annularpassageway from a top portion of the cavity 111 to the externalenvironment when the overpack lid 120 is positioned atop the overpackbody 110 thereby enclosing the top end 151 of the cavity 111.Specifically, the air outlet vent 145 has a vertical section 174 thatextends from the cavity 111 upwardly into the overpack lid 120 in thevertical direction (i.e., the direction of the vertical axis A-A) and ahorizontal section 175 that extends from the vertical section 174 to theannular opening 157 in the horizontal direction (i.e., the directiontransverse to the vertical axis A-A). More specifically, the verticalsection 174 of the air outlet vent 145 extends from an annular opening176 in a bottom surface 177 of the overpack lid 120 and the horizontalsection 175 extends from the vertical section 174 to the annular opening157 in the outer sidewall surface 178 of the overpack lid 120. Asdescribed above, the annular opening 157 is a circumferential openingthat extends around the entirety of the overpack lid 120 in a continuousand uninterrupted manner and circumferentially surrounds the verticalaxis A-A.

The overpack body 110 additionally comprises a bottom block 160 disposedwithin the cylindrical wall 112, and more specifically within the innershell 113 of the cylindrical wall 112, and a base structure at a bottomend 179 of the cylindrical wall 112. The base structure comprises a baseplate 161 and an annular plate 162. The air inlet vent 140 is formeddirectly into the bottom block 160, which is a thick sandwich of steeland concrete. The bottom block 160 is positioned below the floor 152 ofthe cavity 111. More specifically, the bottom block 160 extends betweenthe floor 152 of the cavity 111 and the base plate 161, which forms thebottom end of the VVO 100. The bottom block 160 has a columnar portion163 and a horizontal portion 164.

The annular plate 162 is a donut-shaped plate having a central hole 181.The annular plate 162 is axially spaced from the base plate 161, therebycreating a space or gap in between the annular plate 162 and the baseplate 161. Moreover, the annular plate 162 extends from the outersurface 117 of the overpack body 110 inwardly towards the vertical axisA-A a radial distance that is less than the radius of the overpack body110. More specifically, the annular plate 162 extends from the outersurface 117 of the overpack body 110 to the columnar portion 163 of thebottom block 160. Thought of another way, the columnar portion 163 ofthe bottom block 160 extends through the central hole 181 of the annularplate 162 and rests atop the base plate 161.

Referring to FIGS. 1, 4, 6 and 8 concurrently, the air inlet vent 140will be described in more detail. In the exemplified embodiment, the airinlet vent 140 is formed into the bottom closure plate 130 and extendsinto the bottom block 160 and comprises an annular air inlet plenum 141and an annular air inlet passageway 142. The annular air inlet plenum141 is formed in the space/gap between the annular plate 162 and thebase plate 161. Thus, the annular air inlet plenum 141 is substantiallyhorizontal and extends radially inward from the outer surface 117 of theoverpack body 110. More specifically, the annular air inlet plenum 141extends horizontally from the outer surface 117 of the overpack body 110at an axial height below the floor 152 of the cavity 111. An opening 143is formed in the outer surface 117 of the overpack body 110 that forms apassageway from the external environment to the annular air inlet plenum141 to enable cool air to enter into the annular air inlet plenum 141from the external environment as has been described above. The opening143 circumferentially surrounds the vertical axis A-A around theentirety of the outer surface 117 of the overpack body 110 in anuninterrupted and continuous manner. In other words, the opening 143 isa substantially 360° opening in the outer surface 117 of the overpackbody 110.

The annular air inlet passageway 142 extends upward from a top surface144 of the annular air inlet plenum 141 to the floor 152 of the cavity111. More specifically, the annular air inlet passageway 142 extendsupwardly from an opening 147 in the top surface 144 of the annular airinlet plenum 141 to an opening 146 in the floor 152. The annular airinlet passageway 142 is wholly formed within the bottom block 160. Theopening 147 in the top surface 144 of the annular air inlet plenum 141is proximate an end of the annular air inlet plenum opposite the opening143 in the outer surface 117 of the overpack body 110. The opening 146in the floor 152 is an annular opening that extends 360° around thefloor 152.

The annular air inlet plenum 141 circumferentially surrounds thevertical axis A-A. In the exemplified embodiment, the annular air inletpassageway 142 also circumferentially surrounds the vertical axis A-Aand has an inverted truncated cone shape. Thus, the annular air inletpassageway 142 extends upward from the air inlet plenum 141 to theopening 146 in the floor 152 of the cavity 111 at an oblique anglerelative to the vertical axis A-A. Thought of another way, the annularinlet passageway 142 extends from the air inlet plenum 141 at a firstend 183 to the floor 152 at a second end 184. The first end 183 islocated a first radial distance R₁ from the vertical axis A-A and thesecond end 184 is located a second radial distance R₂ from the verticalaxis A-A. The second radial distance R₂ is greater than the first radialdistance R₁. Of course, the invention is not to be so limited and incertain other embodiments the annular air inlet passageway 142 can takeon other shapes as desired.

Referring to FIGS. 1, 4, 7 and 8 concurrently, the annular air inletplenum 141 will be further described. The annular air inlet plenum 141comprises a plurality of plates 148 therein. Each of the plates 148extends from a first end 149 to a second end 159. The first ends 149 ofthe plates 148 are proximate the outer surface 117 of the overpack body110 and the second ends 159 of the plates 148 are proximate the columnarportion 163 of the bottom block 160. A line connecting the first ends149 of the plates 148 forms a first reference circle 171 having adiameter D₁ and a line connecting the second ends 159 of the plates 148forms a second reference circle 172 having a diameter D₂, wherein thefirst diameter D₁ is greater than the second diameter D₂.

Each of the plates 148 in the annular air inlet plenum 141 extend alonga reference line 169 that is tangent to a third reference circle 170.Although the reference line 169 is only illustrated with regard to twoof the plates 148, it should be understood that each of the plates has areference line that is tangent to the third reference circle 170. Thecircumference of the third reference circle 170 is formed by an outersurface 165 of the columnar portion 163 of the bottom block 160. Thethird reference circle 170 has a center point that is coincident withthe vertical axis A-A. In the exemplified embodiment, the plates 148 arethin steel plates that facilitate transferring the weight of the VVO 100to the base plate 161 and also provide a means to scatter and absorb anyerrant gamma radiation that may attempt to exit the air inlet plenum.Furthermore, in the exemplified embodiment sixty plates 148 areillustrated. However, the invention is not to be so limited and incertain other embodiments more or less than sixty plates 148 may bedisposed within the annular air inlet plenum 141.

Due to the axisymmetric configuration of the air inlet plenum 141, theannular air inlet vent 140 is configured so that aerodynamic performanceof the air inlet vent 140 is independent of an angular direction of ahorizontal component of an air-stream applied to the outer surface 117of the overpack body 101. Similarly, due to the axisymmetricconfiguration of the air outlet vent 145, the air outlet vent 145 isconfigured so that the aerodynamic performance of the air outlet vent145 is independent of an angular direction of a horizontal component ofan air-stream applied to the outer surface 117 of the overpack body 110.

II. Inventive Concept 2

With reference to FIGS. 9-26, a second inventive concept will bedescribed.

The present invention provides a separate, reusable shielded lifting lidfor waste canister lid bolting and lifting. Accordingly, the lifting lidis bolted and not welded to the canister. The canister loading is dry inan overpack such as a metal cylindrical jacket holding the radioactivewaste inside. Canisters typically have thick (e.g. 10 inch) steel lidson each canister to protect the operator from radiation during canisterclosure operations. The thick lids are heavy and expensive, and furthernot reusable as they remain attached to the canister for longer-termstorage.

Advantageously, the present invention allows use of a significantlythinner main closure confinement lid (e.g. about 3 to 5-inch thick inexemplary embodiments) for radionuclides containment. After radioactivewaste contents are placed in the canister, the confinement lid isinstalled and held in place by gravity alone in some embodiments. Theconfinement lid thickness, however, has generally poor radiationshielding value. Accordingly, the confinement lid is installed using athicker and reusable shielded lifting lid which serves as an upperover-lid to the lower confinement lid. The two-part lid systemcombination of the confinement lid and shielded lifting lid provide thethickness required to shield the operator from the radioactive canistercontents during the canister closure bolting operations.

In use, the shielded lifting lid in one exemplary and non-limitingembodiment has holes that match the bolt spacing to allow the operatorto install the confinement lid bolts in a radiation shieldedenvironment. After the lifting lid bolts are installed, the operatorhooks up the lifting rigging to the shielded lifting lid and moves awayfrom the canister to a more distal and remote location. The shieldedlifting lid may then be removed from the top of the canister, preferablywith the confinement lid remaining in place, and a heavy overpack lid isinstalled for longer term storage and radiation shielding. Using thismethod, the waste canister and overpack advantageously are shorter,lighter, better shielded, and less expensive to fabricate.

FIGS. 9 and 10 depict a radioactive canister system according to thepresent disclosure including a waste canister 1100 having a generallycylindrical body defining an interior chamber 1101 and comprised of atop 1102, bottom 1104, and cylindrical sidewall 1106 extendingtherebetween. Top 1102 is open for insertion of radioactive waste andbottom 1104 is preferably closed in one embodiment. A main closureconfinement lid 1200 is shown attached to top 1102 of canister 1100 by aplurality of fasteners such as mounting bolts 1154 which may becircumferentially spaced apart around the top of the canister, asfurther described herein. In one embodiment, canister 1100 may be anon-fuel radioactive waste canister (NWC).

Referring to FIG. 10, canister 1100 has an interior configured to storethe size and shape of radioactive waste to be deposited in the canister.In one embodiment, the canister may include a basket insert 1120configured for holding a plurality of metal waste cylinders 1121 (see,e.g. FIG. 14) each containing radioactive waste materials. Basket insert1120 includes a pair of vertically spaced apart top and bottom plates1122, 1124 which are connected via a plurality of tie rods 1126. Topplate 1122 and bottom plate 1124 include a plurality of horizontallyspaced apart circular openings 1123 each having a diameter which isconfigured and dimensioned to receive waste cylinders 1121 therethrough,as shown in FIG. 14.

Referring to FIGS. 10 and 11, the top portion of tie rods 1126 may bethreaded for attachment to top plate 1122 by a threaded nut 1125. Topplate 1122 may be spaced by a vertical distance below the top 1102 ofcanister 1100. Bottom plate 1124 may be elevated by a vertical distanceabove the bottom 1104 of canister 1100 by a plurality of verticaltubular sleeves 1128 having a bottom end resting on bottom 1104 of thecanister 1100 and a top end attached to bottom plate 1124 as bettershown in FIG. 12. In one embodiment, sleeves have an inside diametersized to receive the bottom end portion of tie rods 1126 which areslidably received in the sleeves. This provides for vertical adjustmentin the height of the basket insert 1120 to accommodate the height ofwaste cylinders 1121 to be stored inside canister 1100. Bottom plate1124 remains fixed and stationary in position. The top plate 1122 withattached tie rods 1126, however, is movable upwards and downwards withrespect to the canister and bottom plate 1124 to reach a desiredposition depending on the height of waste cylinders 1121. In someembodiments, the top plate 1122 may be thereafter be fixed in thedesired position after vertical adjustments are made by securing the topplate to the interior of the canister sidewall 1106 such as by weldingor other suitable means. Accordingly, adjustable basket insert 1120 mayaccommodate a variety of waste cylinder heights.

Basket insert 1120 (i.e. top plate, bottom plate, tie rods, etc.) may bemade of any suitable material, including without limitation a corrosionresistant metal such as stainless steel in one embodiment.

FIG. 13 shows canister 1100 loaded into an outer overpack 1130 fortransport and storage of radioactive waste. The overpack providesprotection during transport and storage of the waste by encapsulatingthe waste canister in an outer protective jacket. Overpack 1130 has anopen top 1132, and is configured and dimensioned to completely receivecanister 1100 through the top 1102. Overpack 1130 has an open interiordefining an interior surface 1133 and an exterior surface 1135 (see alsoFIG. 17). Overpack 1130 is generally cylindrical in shape furtherincluding a cylindrical sidewall 1134 and flat closed bottom 1136 (seeFIG. 23) configured for resting on a flat surface such as concrete slab.Preferably, in one embodiment, overpack 1130 has a greater height thancanister 1100 so that the canister is recessed below the open top 1132of the overpack when fully inserted therein.

Overpack 1130 may be made of any suitable material or combination ofmaterials (see, e.g. FIG. 17) which may include neutron absorbingmaterials such as without limitation concrete, lead, or boron. Anexample of a suitable overpack for use with canister 1100 may be aHI-SAFE™ transport overpack as used in vertical non-fuel waste storagesystems available from Holtec International of Marlton, NJ. Thesidewalls 1134 forming the spaced apart cylindrical walls that define anannular space between the inner and outer surfaces 1133 and 1135respectively may be formed of a corrosion resistant metal also selectedfor strength to protect the inner canister 1100, such as stainless steelas one non-limiting example. The neutron absorbing material may bedisposed between the inner and outer surfaces 1133 and 1135. In someembodiments, overpack 1130 may also include Metamic® for radiationshielding which is a discontinuously reinforced aluminum/boron carbidemetal matrix composite material also available from HoltecInternational.

Referring to FIGS. 10-11 and 13, the top of the canister 1100 mayinclude a peripheral contamination boundary seal which cooperates withthe confinement lid 1200 to prevent leakage of radiation from thecanister, particularly at the lid bolting locations. In particular, theboundary seal shields the mounting blocks 1150 to prevent radiationstreaming.

In one embodiment, the boundary seal may be configured as an annularshielding flange 1140 that extends circumferentially around the upperperipheral edge of the top 1102 of the canister. Confinement lid 1200rests on the shielding flange when bolted to the canister 1100.Shielding flange 1140 may be horizontally flat and extend inwards in adirection perpendicular to and from sidewall 1106 towards the verticalaxial centerline CL of the canister 1100. In one embodiment, shieldingflange 1140 is attached to the uppermost top edge of the sidewall 1106as shown. Shielding flange 1140 may have an at least partially scallopedconfiguration in top plan view in some embodiments as shown toaccommodate insertion of waste cylinders 1121 into the canister.According, the scallops 1142 if provided are preferably concentricallyaligned with the circular openings 1123 in basket insert 1120 in topplan view. This minimizes the required diameter of the canister 1100 forholding the waste cylinders 1121. In other possible embodiments,however, shielding flange 1140 may have an uninterrupted shape forming acontinuous ring in top plan view.

At the lid bolting locations, shielding flange 1140 is configured tocover a with a plurality of mounting blocks 1150 which arecircumferentially spaced around the interior of canister 1100 disposedadjacent to sidewall 1106 to provide a radiation-shielded bolting systemfor attaching confinement lid 1200 and shielded lifting lid 1300 to thecanister. Shielding flange 1140 may be formed of any suitable materialincluding metals which are corrosion resistant such as stainless steel.

With continuing reference to FIGS. 10-11 and 13, mounting blocks 1150may have a generally arcuate and curved shape in top plan view whichcomplements the inside radius of curvature of the sidewall 1106 to whichmounting blocks 1150 may be attached. Mounting blocks 1150 may berigidly/fixedly attached to the canister sidewall 1106 by a suitablystrong mechanical connection capable of supporting at least the entiredead weight of canister 1100 and basket insert 1120 for lifting andloading the canister into overpack 1130. Accordingly, in one preferredembodiment, mounting blocks 1150 are welded to at least sidewall 1106 ofthe canister body for strength. In some embodiments, the mounting blocks1150 may be abutted against but are not fixedly connected to theunderside of radiation shielding flange 1140 so that lifting loads arenot transferred to the flange directly but rather bypass the flange tothe mounting blocks 1150 via the bolting provided.

Any suitable number of mounting blocks 1150 may be provided; the numberand circumferential spacing being dependent on the magnitude of thestructural load imparted to the blocks dependent on whether the canister1100 will be lifted in an empty condition or in a fully loaded conditionwith filled waste cylinders 1121 positioned in the canister. It is wellwithin the ambit of those skilled in the art to determine an appropriatenumber and circumferential spacing of the mounting blocks 1150.

In one embodiment, the mounting blocks 1150 are each configured for bothlifting canister 1100 and attaching both the lower confinement lid 1200and upper lifting lid 1300. As best shown in FIGS. 11 and 17, mountingblocks 1150 each include a plurality of threaded mounting sockets 1152for forming a threaded connection with complementary threaded mountingbolts 1154 and 1156 used for attaching confinement lid 1200 and shieldedlifting lid 1300 respectively to the canister 1100. In one non-limitingexample, three threaded mounting sockets 1152 may be provided in eachmounting block. However, other suitable numbers of mounting sockets maybe used. In certain embodiments, the mounting sockets 1152 extend onlypartially into the mounting blocks 1150 as shown. Radiation shieldingflange 1140 includes mating holes 1144 which are each concentricallyaligned with the threaded mounting sockets 1152 of the mounting block toprovide access for mounting bolts 1154, 1156 to the mounting sockets inthe block. Because shielding flange 1140 in some embodiments in notintended to be a load-bearing member relied upon for lifting thecanister, holes 1144 may not be threaded so that the weight of thecanister is transferred through the flange via the mounting bolts 1156to the shielded lifting lid 1300.

In one embodiment, mounting bolts 1154 and/or 1156 may be threaded boltshaving an integral or separate washer disposed adjacent to the head, asbest shown in FIG. 19. Mounting bolts 1154 are used for attaching thelower confinement lid 1200 to canister 1100 via mounting blocks 1150. Inone embodiment, mounting bolts 1154 are not used for lifting thecanister 1100 but rather for lid securement. By contrast, mounting bolts1156 serve a dual purpose and may be used for both attaching the lowershielded lifting lid 1300 to canister 1100 and supporting the weight ofthe canister during lifting operations via mounting blocks 1150 engagedby bolts 1156. In one preferred embodiment, mounting bolts 1156 may havea longer shank than mounting bolts 1154 as shown. This arrangementensures that the depth of threaded engagement between the threadedmounting sockets 1152 of the mounting blocks 1150 and mounting bolt 1156is sufficient for lifting the canister 1100, as further explainedherein.

The confinement lid 1200 is generally circular in shape (top plan view)and shown in FIGS. 8, 17, and 19. Confinement lid 1200 includes aplurality of bolt holes 1202 spaced circumferentially around theperipheral side 1204 of the lid as best shown in FIG. 9 (including atlocations where mounting bolts 1154 are shown installed). Bolt holes1202 penetrate top surface 1206 of the confinement lid, and in oneembodiment are not threaded. The bolt holes 1202 may be arranged ingroups corresponding to the location and arrangement of the mountingblocks 1150 inside the canister 1100. The bolt holes 1202 have adiameter sized to at least pass the shank of mounting bolts 1154 and1156 through the holes to threadably engage the mounting blocks 1150.Accordingly, some of the bolt holes 1202 are configured to receive theshanks of the confinement lid mounting bolts 1154 and others areconfigured to receive the shank of shielded lifting lid mounting bolts1156. In cases where the mounting bolts 1154 and 1156 have shanks of thesame diameter, the bolt holes 1202 may all have the same diameter. Wherethe shanks of bolts 1154 and 1156 are different in diameter, the holes1202 may have correspondingly different diameters for each bolt.

The confinement lid 1200 may have a uniform thickness from peripheralside 1204 to peripheral side 1204 as best shown in FIG. 17 in oneembodiment. In other embodiments, the thickness may vary at differentlocations on the lid 1200. Confinement lid 1200 may be made of anysuitable material, preferably an appropriate metal for the application.In an exemplary embodiment, without limitation, the confinement lid 1200for example may be made of stainless steel for corrosion resistance.

The upper shielded lifting lid 1300 is not intended to remain oncanister 1100 for longer term waste storage. Instead, in someembodiments, the lifting lid 1300 is configured and structured fortransporting and initially lifting the canister 1100 into position inthe cylindrical overpack 1130 prior to loading the waste cylinders 1121after which the lifting lid is removed, and then after the wastecylinders are loaded in the canister, the lifting lid is replaced on thecanister to shield the operator for bolting the lower confinement lid1200 in place after which the lifting lid is removed again. It will beappreciated that this scenario for using the shielded lifting lid 1300may be varied in other embodiments.

Referring to FIGS. 15-20, shielded lifting lid 1300 is generallycircular in shape (top plan view) and includes a plurality of bolt holes1302 spaced circumferentially around the peripheral side 1304 of the lidas best shown in FIG. 9. In one embodiment, holes 1302 are not threaded.The bolt holes 1302 may be arranged in clustered groups or setscorresponding to the location and arrangement of the mounting blocks1150 inside the canister 1100. The bolt holes 1302 have a diameter sizedto at least pass the shank of mounting bolts 1154 and 1156 through theholes to threadably engage the mounting blocks 1150. Accordingly, someof the bolt holes 1302 are configured to receive the shanks of theconfinement lid mounting bolts 1154 and others are configured to receivethe shank of shielded lifting lid mounting bolts 1156. In cases wherethe mounting bolts 1154 and 1156 have shanks of the same diameter, thebolt holes 1302 may all have the same diameter. Where the shanks ofbolts 1154 and 1156 are different in diameter, the holes 1302 may havecorrespondingly different diameters for each bolt.

According to another aspect of the invention, bolt holes 1302 havedifferent diameters in one embodiment even if the mounting bolts 1154,1156 are used have the same shank diameter. The confinement lid mountingbolts 1154 need not engage the upper shielded lifting lid because bolts1154 are only required to secure the lower confinement lid to canister1100. Accordingly, in the embodiment shown in FIG. 19, the bolt holes1302 for the confinement lid mounting bolts 1154 may have a largerdiameter than the bolt holes 1302 for the lifting lid mounting bolts1156. In this arrangement, the bolt holes 1302 for the confinement lidmounting bolts 1154 are sized with a diameter large enough to allow theshank and entire head of bolts 1154 to pass through the bolt holes sothat the head and integral washer directly engage the top surface 1206of the confinement lid 1200 (see, e.g. FIG. 9). When completelyinstalled, the heads of the mounting bolts 1154 are recessed below thetop surface of the lifting lid 1300 as shown.

By contrast, since the mounting bolts 1156 for the lifting lid 1300 alsoserve a lifting function for the canister 1100, the bolt holes 1302 havea diameter sized so that the heads of bolts 1156 do not pass through thebolt holes and instead engage the top surface 1306 of the lifting lid(thereby projecting above the top surface and remaining exposed as shownin FIG. 19). In this manner, the bolts 1156 transfer the dead load andweight of the canister 1100 from the mounting blocks 1150 directly tothe shielded lifting lid 1300 without involvement of the confinement lid1200. Accordingly, to accommodate the foregoing arrangement, the liftinglid mounting bolts 1156 preferably have a longer shank than theconfinement lid mounting bolts 1154 in this embodiment.

As shown in FIGS. 17 and 18, several spaced apart clusters comprised ofthree bolt holes 1302 may be provided in the non-limiting embodimentshown which are spaced circumferentially around and proximate to theperipheral side 1304 of the shielded lifting lid 1300. Each cluster ofbolt holes 1302 is spaced apart by an arcuate distance from adjacentclusters of holes 1302. The clusters of bolts holes 1302 are eachvertically aligned with a corresponding mounting block 1150 (see alsoFIG. 11). In this embodiment, the center hole 1302 has a smallerdiameter for the lifting lid mounting bolt 1156 than the two adjacentouter holes 1302 have larger diameters for the confinement lid mountingbolts 1154. Other suitable arrangements of holes 1302 may be provided.The bolt holes 1202 in the confinement lid 1200 may also arranged inclusters of three to mate with the bolt holes 1302 of the lifting lid1300. All three of the bolt holes 1202 in each cluster in theconfinement lid, however, may have the same diameter.

Advantageously, having two different size bolt holes 1302 for theconfinement lid mounting bolts 1154 and the lifting lid mounting bolts1156 reduces possible installation error and ensures that the operatorwill not confuse which holes are intended for each. This plays a role indeploying the two-part lid system when the confinement lid 1200 and itsrespective bolts 1154 are eventually left in place after bolting theconfinement lid to the canister 1100 and the lifting lid mounting bolts1156 are removed by the operator, as further described herein.

The shielded lifting lid 1300 may have a non-uniform thickness fromperipheral side 1304 to peripheral side 1304 as best shown in FIG. 17.Accordingly, in one possible embodiment as shown, the peripheral portionof lifting lid 1300 may include an outer annular step or shoulder 1308having a smaller thickness than the inner central portion 1314 of thelid. The shoulder 1308 is configured to complement and abuttingly engagea corresponding top annular rim 1138 of the overpack 1130 such thatportions of the lifting lid 1300 adjacent to peripheral side 1304overlap the top of the rim to prevent radiation streaming as shown. Rim1138 therefore defines an annulus for receiving shoulder 1308.Accordingly, as shown in FIG. 17, shielded lifting lid 1300 has a largerdiameter than confinement lid 1200 to account for the overlap with theannular rim 1138 of the overpack 1130.

The central portion 1314 of the lifting lid 1300 preferably has athickness and a diameter sized to allow at least partial insertion ofthe central portion into the overpack 1130 such that the outwards facingannular sides of the central portion abuts the interior surface 1133 ofthe overpack as shown. This arrangement further prevents radiationstreaming from the canister 1100 when the lifting lid 1300 is in placeon the canister.

Because shielded lifting lid 1300 serves a structural purpose forlifting the canister 1100, the lifting lid preferably has a thicknesswhich is greater than the confinement lid 1200. In one embodiment, thelifting lid has a thickness which is at least twice the thickness of theconfinement lid. Shielded lifting lid 1300 may be made of any suitablematerial, preferably an appropriate metal for the application. Inexemplary embodiments, without limitation, the lifting lid 300 forexample may be made of carbon steel or stainless steel.

Referring to FIGS. 15 and 16, the lower confinement lid 1200 isdetachably mounted to upper shielded lifting lid 1300 so that the lidassembly 1200/1300 may be lifted and moved as a single unit as shownwith the lifting lid supporting the confinement lid when not attached tothe canister 1100. When needed during the canister closure operations,the lifting lid 1300 may be uncoupled from the confinement lid 1200. Inone embodiment, a plurality of circumferentially spaced fasteners suchas threaded assembly bolts 1131 may be provided to attach lifting lid1300 to confinement lid 1200. Assembly bolts 1131 which are insertedthrough the lifting lid 1300 and engage complementary threaded sockets1208 (shown in FIG. 9) formed in the confinement lid (such arrangementand operation being apparent to those skilled in the art without furtherelaboration). A suitable number of assembly bolts 1131 are provided tosupport the lower confinement lid 1200 from the upper shielded liftinglid 1300 during hoisting. Accordingly, confinement lid 1200 may beconsidered to be fully supported by the lifting lid 1300 during liftingof the lid assembly 1200/1300.

As shown in FIGS. 15 and 16, shielded lifting lid 1300 includes alifting attachment such as lifting lugs 1402 and pin 1404 for grapplingand hoisting the lid. Other suitable lifting attachments configured forgrappling such as for example lifting bails may be used.

An exemplary method for storing radioactive waste using the presentcontainer system with two-part lid assembly 1200/1300 (confinement lid1200, lifting lid 1300) according to the present disclosure will now bedescribed. As a preliminary step, the lower confinement lid 1200 isdetachably mounted to the upper shielded lifting lid 1300 using assemblybolts 1131 to collectively form the lid assembly 1200/1300, shown inFIG. 15.

Referring to FIGS. 9 and 10, the method begins with a canister 1100first being provided with an empty basket insert 1120 disposed insidethe canister as shown. Next, the empty canister 1100 is lifted andplaced into the overpack 1130 as shown in FIG. 13. In one embodiment,this step may be performed by bolting the lid assembly 1200/1300 tocanister 1100 using the mounting bolts 1156 to threadably engage themounting blocks 1150, and grappling and attaching a hoist 1400 to theupper lifting lid 1300 using lifting lugs 1402 and pin 1404 as shown inFIG. 15. The hoist 1400 may be part of the lifting equipment such as acrane or other suitable equipment operable to raise and lower thecanister. After positioning the basket insert 1120 into the canister1100, the mounting bolts 1156 may be removed to disconnect the canisterfrom the lid assembly. The lid assembly 1200/1300 may then be lifted bythe hoist and removed (see FIG. 13).

Next, one or preferably more lid alignment pins 1406 may be threadedinto some of the threaded sockets 1152 of the mounting block toeventually help properly align the lid assembly 1200/1300 with thecanister (see FIG. 13). In one non-limiting example, three alignmentpins 1406 are used spaced apart on the canister. The alignment pins 1406are preferably installed locally by an operator prior to loading theradioactively “hot” waste cylinders 1121 into the canister. Followinginstallation of the alignment pins 1406, the waste cylinders 1121 areloaded into the canister 1100, and more specifically positioned in theirrespective locations provided in basket insert 1120 as shown in FIG. 14.Loading of the waste cylinders is performed remotely (i.e. at adistance) by an operator using suitable equipment to protect theoperator from radiation.

After loading the waste cylinders 1121, the lid assembly 1200/1300 isremotely hoisted by the operator over and vertically positioned abovethe top 1102 of the canister 1100, as shown in FIG. 15. Using the lidalignment pins 1406, the operator vertically aligns holes 1302 inshielded lifting lid (with holes 1202 in confinement lid beingconcentrically aligned with holes 1302) with corresponding pins 1406 toproperly orient the lid rotationally with respect to the canister. Whenthe pins 1406 and their corresponding holes have been axially aligned,the operator lowers lid assembly 1200/1300 onto the canister 1100 asshown in FIG. 16 (see pins 1406 extending through holes 1302). Theoperator will now be shielded from radiation emitted from the canisterso that the confinement lid 1200 may be bolted in place locally.

Next, the lid alignment pins 1406 and assembly bolts 1131 which hold thelower confinement lid 1200 to upper shielded lifting lid 1300 may beremoved (see, e.g. FIG. 18). All of the confinement lid mounting bolts1154 may then be installed to mount the confinement lid 1200 to thecanister 1100 using the mounting blocks 1150. The mounting bolts 1154are threaded through bolt holes 1302 until the heads of the bolts engagethe top surface 1206 of the confinement lid 1200 and the bolts aretightened to the required torque (see FIGS. 19 and 20).

Prior to removing the shielded lifting lid 1300, a set of overpack lidalignment pins 1408 may next be installed in threaded sockets 1510 ofthe overpack 1130.

With the confinement lid 1200 now fully fastened to canister 1100, theshielded lifting lid 1300 may next be removed via the hoist remotely byan operator as shown in FIG. 23.

In the following steps, the overpack lid 1500 is installed on overpack1130 following closure of canister 1100 described above. FIG. 23 showsthe shielded lifting lid 1300 being removed and the overpack lid 1500staged for installation. FIG. 21 shows overpack lid 1500 in greaterdetail. Overpack lid 1500 is circular in shape (top plan view) andincludes a plurality of mounting holes 1502, top surface 1504,peripheral sides 1506, and a lifting bail 1508 attached towards thecenter of the lid for engagement by a hoist. Overpack lid 1500 serves astructural role of protecting the canister 1100 disposed inside theoverpack 1130, and in some embodiments supporting the weight of theoverpack when mounted thereto for transport and lifting. Accordingly,overpack lid 1500 may have a thickness greater than the thickness of theconfinement lid 1200.

Referring now to FIGS. 23 and 24, the overpack lid 1500 is grappled andlifted via the attached hoist 1400 by crane or other equipment,vertically aligned with overpack 1130 using the alignment pins 1408 in amanner similar to alignment pins 1406, and lowered onto the overpack.Alignment pins 1408 are then removed and mounting bolts 1512 are theninstalled in the threaded sockets 1510 of the overpack 1130 to completeinstallation and securement of the overpack lid 1500, as shown in FIG.25. Optionally, the lifting bail 1508 may be removed.

FIG. 26 shows the overpack 1130 with overpack lid 1500 fully installedand canister 1100 disposed inside loaded with waste cylinders 1121.Protective caps 1514 may be installed over mounting bolts 1512. Anoperator is shown in FIG. 26 to provide perspective on the size ofoverpack 1130 in one non-limiting embodiment, which may be about 6 ormore feet in diameter and about 6 or more feet in height. Any suitablesize overpack may be used.

As noted herein, the shielded lifting lid 1300 is reusable. Accordingly,in some embodiments, the exemplary method described above may furthercomprise a step of detachably mounting a second different confinementlid 1200 to the shielded lifting lid 1300; the second confinement lidand shielded lifting lid collectively forming a second lid assembly.

It will be appreciated that the two-part lid assembly 1200/1300 may alsobe used in applications where the confinement lid 1200 is intended to bewelded to the canister 1100 for closure rather than by bolting.

III. Inventive Concept 3

With reference to FIGS. 27-34, a third inventive concept will bedescribed.

FIG. 27A illustrates a high level waste (“HLW”) storage container 2010,encased in surrounding concrete 2011, as it would be in an installation.FIG. 28 illustrates the storage container 2010 in a sectional view,still with the surrounding concrete 2011. While the HLW storagecontainer 2010 will be described in terms of being used to store acanister of spent nuclear fuel, it will be appreciated by those skilledin the art that the systems and methods described herein can be used tostore any and all kinds of HLW.

The HLW storage container 2010 is designed to be a vertical, ventilateddry system for storing HLW such as spent fuel. The HLW storage container2010 is fully compatible with 100 ton and 125 ton transfer casks for HLWtransfer procedures, such as spent fuel canister transfer operations.All spent fuel canister types engineered for storage in free-standing,below grade, and/or anchored overpack models can be stored in the HLWstorage container 2010.

As used in this section the term “canister” broadly includes any spentfuel containment apparatus, including, without limitation, multi-purposecanisters and thermally conductive casks. For example, in some areas ofthe world, spent fuel is transferred and stored in metal casks having ahoneycomb grid-work/basket built directly into the metal cask. Suchcasks and similar containment apparatus qualify as canisters, as thatterm is used herein, and can be used in conjunction with the HLW storagecontainer 2010 as discussed below.

The HLW storage container 2010 can be modified/designed to be compatiblewith any size or style of transfer cask. The HLW storage container 2010can also be designed to accept spent fuel canisters for storage at anIndependent Spent Fuel Storage Installations (“ISFSI”). ISFSIs employingthe HLW storage container 2010 can be designed to accommodate any numberof the HLW storage container 2010 and can be expanded to add additionalHLW storage containers 2010 as the need arises. In ISFSIs utilizing aplurality of the HLW storage container 2010, each HLW storage container2010 functions completely independent form any other HLW storagecontainer 2010 at the ISFSI.

The HLW storage container 2010 has a body 2020 and a lid 2030. The lid2030 rests atop and is removable/detachable from the body 2020. Althoughan HLW storage container can be adapted for use as an above gradestorage system, by incorporating design features found in U.S. Pat. No.7,933,374, this HLW storage container 2010, as shown, is designed foruse as a below grade storage system.

Referring to FIG. 28, the body 2020 includes an outer shell 2021 and aninner shell 2022. The outer shell 2021 surrounds the inner shell 2022,forming a space 2023 therebetween. The outer shell 2021 and the innershell 2022 are generally cylindrical in shape and concentric with oneanother. As a result, the space 2023 is an annular space. While theshape of the inner and outer shells 2022, 2021 is cylindrical in theillustrated embodiment, the shells can take on any shape, includingwithout limitation rectangular, conical, hexagonal, or irregularlyshaped. In some embodiments, the inner and outer shells 2022, 2021 willnot be concentrically oriented.

The space 2023 formed between the inner shell 2022 and the outer shell2021 acts as a passageway for cool air. The exact width of the space2023 for any HLW storage container 2010 is determined on a case-by-casedesign basis, considering such factors as the heat load of the HLW to bestored, the temperature of the cool ambient air, and the desired fluidflow dynamics. In some embodiments, the width of the space 2023 will bein the range of 1 to 6 inches. While the width of space 2023 can varycircumferentially, it may be desirable to design the HLW storagecontainer 2010 so that the width of the space 2023 is generally constantin order to effectuate symmetric cooling of the HLW container and evenfluid flow of the incoming air. As discussed in greater detail below,the space 2023 may be divided up into a plurality of passageways.

The inner shell 2022 and the outer shell 2021 are secured atop a floorplate 2050. The floor plate 2050 is hermetically sealed to the outershell 2021, and it may take on any desired shape. A plurality of spacers2051 are secured atop the floor plate 2050 within the space 2023. Thespacers 2051 support a pedestal 2052, which in turn supports a canister.When a canister holding HLW is loaded into the cavity 2024 for storage,the bottom surface of the canister rests atop the pedestal 2052, formingan inlet air plenum between the underside of the pedestal 2052 and thefloor of cavity 2024. This inlet air plenum contributes to the fluidflow and proper cooling of the canister.

Preferably, the outer shell 2021 is seal joined to the floor plate 2050at all points of contact, thereby hermetically sealing the HLW storagecontainer 2010 to the ingress of fluids through these junctures. In thecase of weldable metals, this seal joining may comprise welding or theuse of gaskets. Most preferably, the outer shell 2021 is integrallywelded to the floor plate 2050.

An upper flange 2077 is provided around the top of the outer shell 2021to stiffen the outer shell 2021 so that it does not buckle orsubstantially deform under loading conditions. The upper flange 2077 canbe integrally welded to the top of the outer shell 2021.

The inner shell 2022 is laterally and rotationally restrained in thehorizontal plane at its bottom by support legs 2027 which straddle lowerribs 2053. The lower ribs 2053 are preferably equispaced about thebottom of the cavity 2024. The inner shell 2022 is preferably not weldedor otherwise permanently secured to the bottom plate 2050 or outer shell2021 so as to permit convenient removal for decommissioning, and ifrequired, for maintenance.

The inner shell 2022, the outer shell 2021, the floor plate 2050, andthe upper flange 2077 are preferably constructed of a metal, such as athick low carbon steel, but can be made of other materials, such asstainless steel, aluminum, aluminum-alloys, plastics, and the like.Suitable low carbon steels include, without limitation, ASTM A516, Gr.70, A515 Gr. 70 or equal. The desired thickness of the inner and outershells 2022, 2021 is matter of design choice and will determined on acase-by-case basis.

The inner shell 2022 forms a cavity 2024. The size and shape of thecavity 2024 is also a matter of design choice. However, it is preferredthat the inner shell 2022 be designed so that the cavity 2024 is sizedand shaped so that it can accommodate a canister of spent nuclear fuelor other HLW. While not necessary, it is preferred that the horizontalcross-sectional size and shape of the cavity 2024 be designed togenerally correspond to the horizontal cross-sectional size and shape ofthe canister-type that is to be used in conjunction with a particularHLW storage container. More specifically, it is desirable that the sizeand shape of the cavity 2024 be designed so that when a canistercontaining HLW is positioned in the cavity 2024 for storage (asillustrated in FIG. 30A), a small clearance exists between the outerside walls of the canister and the side walls of the cavity 2024.

Designing the cavity 2024 so that a small clearance is formed betweenthe side walls of the stored canister and the side walls of the cavity2024 limits the degree the canister can move within the cavity during acatastrophic event, thereby minimizing damage to the canister and thecavity walls and prohibiting the canister from tipping over within thecavity. This small clearance also facilitates flow of the heated airduring HLW cooling. The exact size of the clearance can becontrolled/designed to achieve the desired fluid flow dynamics and heattransfer capabilities for any given situation. In some embodiments, forexample, the clearance may be 1 to 3 inches. A small clearance alsoreduces radiation streaming.

The inner shell 2022 is also equipped with multiple sets of equispacedlongitudinal ribs 2054, 2055, in addition to the lower ribs 2053discussed above. One set of ribs 2054 are preferably disposed at anelevation that is near the top of a canister of HLW placed in the cavity2024. This set of ribs 2054 may be shorter in length in comparison tothe height of the cavity 2024 and a canister. Another set of ribs 2055are set below the first set of ribs 2054. This second set of ribs 2055is more elongated than the first set of ribs 2054, and these ribs 2055extend to, or nearly to, the bottom of the cavity 2024. These ribs 2053,2054, 2055 serve as guides for a canister of HLW is it is lowered downinto the cavity 2024, helping to assure that the canister properly restsatop the pedestal 2052. The ribs also serve to limit the canister'slateral movement during an earthquake or other catastrophic event to afraction of an inch.

A plurality of openings 2025 are provided in the inner shell 2022 at ornear its bottom between the support legs 2027. Each opening 2025provides a passageway between the annular space 2023 and the bottom ofthe cavity 2024. The openings 2025 provide passageways by which fluids,such as air, can pass from the annular space 2023 into the cavity 2024.The openings 2025 are used to facilitate the inlet of cooler ambient airinto the cavity 2024 for cooling a stored HLW having a heat load. Asillustrated, eight openings 2025 are equispaced about the bottom of theinner shell 2022. However, any number of openings 2025 can be included,and they may have any spacing desired. The exact number and spacing willbe determined on a case-by-case basis and will be dictated by suchconsiderations as the heat load of the HLW, desired fluid flow dynamics,etc. Moreover, while the openings 2025 are illustrated as being locatedin the side wall of the inner shell 2022, the openings can be providedin the floor plate in certain modified embodiments of the HLW storagecontainer.

The openings 2025 in the inner shell 2022 are sufficiently tall toensure that if water enters the cavity 2024, the bottom region of acanister resting on the pedestal 2052 would be submerged for severalinches before the water level reaches the top edge of the openings 2025.This design feature helps ensure thermal performance of the system underaccidental flooding of the cavity 2024.

With reference to FIG. 29, a layer of insulation 2026 is provided aroundthe outside surface of the inner shell 2022 within the annular space2023. The insulation 2026 is provided to minimize heating of theincoming cooling air in the space 2023 before it enters the cavity 2024.The insulation 2026 helps ensure that the heated air rising around acanister situated in the cavity 2024 causes minimal pre-heating of thedowndraft cool air in the annular space 2023. The insulation 2026 ispreferably chosen so that it is water and radiation resistant andundegradable by accidental wetting. Suitable forms of insulationinclude, without limitation, blankets of alumina-silica fire clay(Kaowool Blanket), oxides of alimuna and silica (Kaowool S Blanket),alumina- silica-zirconia fiber (Cerablanket), and alumina-silica-chromia(Cerachrome Blanket). The desired thickness of the layer of insulation2026 is matter of design and will be dictated by such considerationssuch as the heat load of the HLW, the thickness of the shells, and thetype of insulation used. In some embodiments, the insulation will have athickness in the range ½ to 6 inches.

As shown in FIGS. 28 and 29, inlet ducts 2060 are disposed on the topsurface of the upper flange 2077. Each inlet duct 2060 connects to twoinlet passageways 2061 which continue from under the upper flange 2077,into the space 2023 between the outer and inner shells 2021, 2022, andthen connect to the cavity 2024 by lower openings 2062 in the bottom ofthe inner shell 2022. Within the space 2023, the inlet passageways 2061are separated by dividers 2063 to keep cooling air flowing through eachinlet passageway 2061 separate from the other inlet passageways 2061until the cooling air emerges into the cavity 2024. FIGS. 30A and 30Billustrate the configuration of the inlet passageways 2061 and thedividers 2063. Each inlet passageway 2061 connects with the space 2023by openings 2064 in the top of the outer shell 2021. From the openings2064, the cooling air continues down the in the space, via theindividual inlet passageways 2061 created by the dividers 2064, and intothe cavity 2024, where it is used to cool a placed HLW canister. Thedividers 2063 are equispaced within the space 2023 to aid in balancingthe air pressure entering the space 2023 from each inlet duct and inletpassageway. Also, as shown in the figures, each of the lower ribs 2053is integrated with one of the dividers 2063, such that the lower ribsform an extension of the dividers, extending into the cavity 2024.

Referring back to FIG. 29, each inlet duct 2060 includes a duct cover2065, to help prevent rain water or other debris from entering and/orblocking the inlet passageways 2061, affixed on top of an inlet wall2066 that surrounds the inlet passageways 2061 on the top surface of theupper flange 2077. The inlet wall 2066 is peripherally perforated aroundthe entire periphery of the opening of the inlet passageways 2061. Atleast a portion of the lower part of the inlet ducts are left withoutperforations, to aid in preventing rain water from entering the HLWstorage container. Preferably, the inlet wall 2066 is perforated over60% or more of its surface, and the perforations can be made in anyshape, size, and distribution in accordance with design preferences.When the inlet ducts 2060 are formed with the inlet wall 2066peripherally perforated, each of the inlet ducts has been found tomaintain an intake air pressure independently of each of the other inletducts, even in high wind conditions, and each of the inlet ducts hasbeen found to maintain an intake air pressure substantially the same aseach of the other inlet ducts, again, even in high wind conditions.

The lid 2030 rests atop and is supported by the upper flange 2077 and ashell flange 2078, the latter being disposed on and connected to thetops edge of the inner shell 2022. The lid 2030 encloses the top of thecavity 2024 and provides the necessary radiation shielding so thatradiation does not escape from the top of the cavity 2024 when acanister loaded with HLW is stored therein. The lid 2030 is designed tofacilitate the release of heated air from the cavity 2024.

FIG. 31A illustrates the HLW storage container 2010 with a canister 2013placed within the cavity 2024. As shown in the FIG. 31B detailed view,the bottom of the canister 2013 sits on the pedestal 2052, and the lowerribs 2053 maintain a space between the bottom of the canister 2013 andthe inner shell 2022. Similarly, the FIG. 31C detailed view shows thatthe upper ribs 2054 maintain a space between the top of the canister2013 and the inner shell 2022.

The FIG. 31D detailed view shows the lid 2030 resting atop the upperflange 2077 and the shell flange 2078. The lid 2030 includes a closuregasket 2031 which forms a seal against the upper flange 2077 when the201id 30 is seated, and a leaf spring gasket 2032 which forms a sealagainst the shell flange 2078.

FIGS. 32 and 33 illustrate the lid 2030 removed from the body of the HLWstorage container. Referring first to FIG. 32, the lid 2030 ispreferably constructed of a combination of low carbon steel and concrete(or another radiation absorbing material) in order to provide therequisite radiation shielding. The lid 2030 includes an upper lid part2033 and a lower lid part 2034. The upper lid part 2033 preferableextends at least as high as, if not higher than, the top of each inletduct 2060. Each lid part 2033, 2034 includes an external shell 2035,2036 encasing an upper concrete shield 2037 and a lower concrete shield2038. One or more outlet passageways 2039 are formed within and aroundthe body parts 2033, 2034 to connect the cavity with the outlet duct2040 formed on the top surface of the lid 2030. The outlet passageways2039 pass over the lower lid part 2034, between the upper and lower lidparts 2033, 2034, and up through a central aperture within the upper lidpart 2034. The outlet duct 2040 covers this central aperture to bettercontrol the heated air as it rises up out of the. By being disposed onthe top of the lid 2030, the outlet duct 2040 may also be raised upsignificantly higher than the inlet ducts, using any desired length ofextension for the outlet duct. By raising up the outlet duct higher,mixing between the heated air emitted from the outlet duct and coolerair being drawn into the inlet ducts can be significantly reduced, ifnot eliminated altogether.

The outlet duct 2040, which is constructed similar to the inlet ducts,includes a duct cover 2041, to help prevent rain water or other debrisfrom entering and/or blocking the outlet passageways 2039, affixed ontop of an outlet wall 2042 that surrounds the outlet passageways 2039 onthe top surface of the upper lid part 2033. The outlet wall 2042 isperipherally perforated around the entire periphery of the opening ofthe outlet passageways 2039. At least a portion of the lower part of theoutlet duct is left without perforations, to aid in preventing rainwater from entering the HLW storage container. Preferably, the outletwall 2042 is perforated over 60% or more of its surface, and theperforations can be made in any shape, size, and distribution inaccordance with design preferences.

The external shell of the lid 2030 may be constructed of a wide varietyof materials, including without limitation metals, stainless steel,aluminum, aluminum-alloys, plastics, and the like. The lid may also beconstructed of a single piece of material, such as concrete or steel forexample, so that it has no separate external shell.

When the lid 2030 is positioned atop the body 2020, the outletpassageways 2039 are in spatial cooperation with the cavity 2024. As aresult, cool ambient air can enter the HLW storage container 2010through the inlet ducts 2060, flow into the space 2023, and into thebottom of the cavity 2024 via the openings 2062. When a canistercontaining HLW having a heat load is supported within the cavity 2024,this cool air is warmed by the HLW canister, rises within the cavity2024, and exits the cavity 2024 via the outlet ducts 2040.

Because the inlet ducts 2060 are placed on different sides of the lid2030, and the dividers separate the inlet passageways associated withthe different inlet ducts, the hydraulic resistance to the incoming airflow, a common limitation in ventilated modules, is minimized. Thisconfiguration makes the HLW storage container less apt to build up heatinternally under high wind conditions.

A plurality of HLW storage containers 2100 can be used at the same ISFSIsite and situated in arrays as shown in FIG. 34. Although the HLWstorage containers 2100 are closely spaced, the design permits acanister in each HLW storage container 2100 to be independently accessedand retrieved easily. In addition, the design of the individual storagecontainers 2100, and particularly the design and positioning of theinlet and outlet ducts, enables the inlet ducts of a first of thestorage containers to maintain air pressure independently of the inletducts of a second of the storage containers. Each storage containertherefore will operate independently of each of the other storagecontainers, such that the failure of one storage container is unlikelyto lead directly to the failure of other surrounding storage containersin the array.

IV. Inventive Concept 4

With reference to FIGS. 35-47, a fourth inventive concept will bedescribed.

Referring to FIG. 35, a dual-walled DSC 3099 according to one embodimentof the present invention is disclosed. The dual-walled DSC 3099 and itscomponents are illustrated and described as an MPC style structure.However, it is to be understood that the concepts and ideas disclosedherein can be applied to other areas of high level radioactive wastestorage, transportation and support. Moreover, while the dual-walled DSC3099 is described as being used in combination with a specially designedfuel basket 3090 (which in of itself constitutes an invention), thedual-walled DSC 3099 can be used with any style of fuel basket, such asthe one described in U.S. Pat. No. 5,898,747, issued Apr. 27, 1999. Infact, in some instances it may be possible to use the dual-walled DSC3099 without a fuel basket, depending on the intended function.Furthermore, the dual-walled DSC 3099 can be used to store and/ortransport any type of high level radioactive materials and is notlimited to SNF.

As will become apparent from the structural description below, thedual-walled DSC 3099 contains two independent containment boundariesabout the storage cavity 3030 that operate to contain both fluidic (gasand liquid) and particulate radiological matter within the cavity 3030.As a result, if one containment boundary were to fail, the othercontainment boundary will remain intact. While theoretically the same,the containment boundaries formed by the dual-walled DSC 3099 about thecavity 3030 can be literalized in many ways, including withoutlimitation a gas-tight containment boundary, a pressure vessel, ahermetic containment boundary, a radiological containment boundary, anda containment boundary for fluidic and particulate matter. These termsare used synonymously throughout this application. In one instance,these terms generally refer to a type of boundary that surrounds a spaceand prohibits all fluidic and particulate matter from escaping fromand/or entering into the space when subjected to the required operatingconditions, such as pressures, temperatures, etc.

Finally, while the dual-walled DSC 3099 is illustrated and described ina vertical orientation, it is to be understood that the dual-walled DSC3099 can be used to store and/or transport its load in any desiredorientation, including at an angle or horizontally. Thus, use of allrelative terms through this specification, including without limitation“top,” “bottom,” “inner” and “outer,” are used for convenience only andare not intended to be limiting of the invention in such a manner.

The dual-walled DSC 3099 includes a first shell that acts as an innershell 3010 and a second shell that acts as an outer shell 3020. Theinner and outer shells 3010, 3020 are preferably cylindrical tubes andare constructed of a metal. Of course, other shapes can be used ifdesired. The inner shell 3010 is a tubular hollow shell that includes aninner surface 3011, an outer surface 3012, a top edge 3013 and a bottomedge 3014. The inner surface 3011 of the inner shell 3010 forms acavity/space 3030 for receiving and storing SNF. The cavity 3030 is acylindrical cavity formed about a central axis.

The outer shell 3020 is also a tubular hollow shell that includes aninner surface 3021, an outer surface 3022, a top edge 3023 and a bottomedge 3024. The outer shell 3020 circumferentially surrounds the innershell 3010. The inner shell 3010 and the outer shell 3020 areconstructed so that the inner surface 3021 of the outer shell 3020 is insubstantially continuous surface contact with the outer surface 3012 ofthe inner shell 3010. In other words, the interface between the innershell 3010 and the outer shell 3020 is substantially free of gaps/voidsand are in conformal contact. This can be achieved through an explosivejoining, a cladding process, a roller bonding process and/or amechanical compression process that bonds the inner shell 3010 to theouter shell 3020. The continuous surface contact at the interfacebetween the inner shell 3010 and the outer shell 3020 reduces theresistance to the transmission of heat through the inner and outershells 3010, 3020 to a negligible value. Thus, heat emanating from theSNF loaded within the cavity 3030 can efficiently and effectively beconducted outward through the shells 3010, 3020 where it is removed fromthe outer surface 3022 of the outer shell via convection.

Even though the interface is formed in any of these manners, there stillremains an interstitial space 3097 between the inner shell 3010 and theouter shell 3020. Alternatively, the interstitial space may be formedwithout the inner surface of the outer shell being in substantiallycontinuous surface contact with the outer surface of the inner shell. Asis discussed in more detail below, the presence of this interstitialspace is used advantageously during a leak testing process.

The inner and outer shells 3010, 3020 are preferably both made of ametal. As used herein, the term metal refers to both pure metals andmetal alloys. Suitable metals include without limitation austeniticstainless steel and other alloys including Hastelloy™ and Inconel™. Ofcourse, other materials can be utilized. The thickness of each of theinner and outer shells 3010, 3020 is preferably in the range of 5 mm to25 mm. The outer diameter of the outer shell 3020 is preferably in therange of 1700 mm to 2000 mm. The inner diameter of the inner shell 3010is preferably in the range of 1700 mm to 1900 mm. The specific sizeand/or thickness of the shells 3010, 3020, however, is a matter ofdesign choice.

In some embodiments, it may be further preferable that the inner shell3010 be constructed of a metal that has a coefficient of thermalexpansion that is equal to or greater than the coefficient of thermalexpansion of the metal of which the outer shell 3020 is constructed.Thus, when the SNF that is stored in the cavity 3030 and emits heat, theouter shell 3020 will not expand away from the inner shell 3010. Thisensures that the continuous surface contact between the outer surface3012 of the inner shell 3010 and the outer surface 3021 of the outershell 3020 will be maintained and a gaps will not form under heatloading conditions.

The dual-walled DSC 3099 also includes a first lid that acts as an innertop lid 3060 for the inner shell 3010 and a second lid that acts as anouter top lid 3070 for the second shell 3020. The inner and outer toplids 3060, 3070 are plate-like structures that are preferablyconstructed of the same materials discussed above with respect to theshells 3010, 3020. Preferably the thickness of the inner top lid 3060 isin the range of 99 mm to 300 mm. The thickness of the outer top lid ispreferably in the range of 50 mm to 150 mm. The invention is not,however, limited to any specific dimensions, which will be dictated on acase-by-case basis and the radioactive levels of the SNF to be stored inthe cavity 3030.

Referring to FIG. 36, the inner top lid 3060 includes a top surface3061, a bottom surface 3062 and an outer lateral surface/edge 3063. Theouter top lid 3070 includes a top surface 3071, a bottom surface 3072and an outer lateral surface/edge 3073. When fully assembled, the outerlid 3070 is positioned atop the inner lid 3060 so that the bottomsurface 3072 of the outer lid 3070 is in substantially continuoussurface contact with the top surface 3061 of the inner lid 3060. Theouter lid 3070 also includes a test port 3095, to which one end ofconduit is coupled (see FIGS. 44 and 45) in fluidic communicationtherewith. As is discussed below, the other end of the conduit is fittedwith both a removable seal, to enable leak testing, and valve, bothbeing included to comply with ASME Code.

During an SNF underwater loading procedure, the inner and outer lids3060, 3070 are removed. Once the cavity 3030 is loaded with the SNF, theinner top lid 3060 is positioned so as to enclose the top end of thecavity 3030 and rests atop the brackets 3015. Once the inner top lid3060 is in place and seal welded to the inner shell 3010, the cavity3030 is evacuated/dried via the appropriate method and backfilled withnitrogen, helium or another inert gas. The drying and backfillingprocess of the cavity 3030 is achieved via the holes 3064 of the innerlid 3060 that form passageways into the cavity 3030. Once the drying andbackfilling is complete, the holes 3061 are filled with a metal orotherwise plugged so as to hermetically seal the cavity 3030.

Referring now to FIGS. 35 and 37 concurrently, the outer shell 3020 hasan axial length L₂ that is greater than the axial length L₁ of the innershell 3010. As such, the top edge 3013 of the inner shell 3010 extendsbeyond the top edge 3023 of the outer shell 3020. Similarly, the bottomedge 3024 of the outer shell 3020 extends beyond the bottom edge 3013 ofthe inner shell 3010.

The offset between the top edges 3013, 3023 of the shells 3010, 3020allows the top edge 3013 of the inner shell 3010 to act as a ledge forreceiving and supporting the outer top lid 3070. When the inner lid 3060is in place, the inner surface 3011 of the inner shell 3010 extends overthe outer lateral edges 3063. When the outer lid 3070 is then positionedatop the inner lid 3060, the inner surface 3021 of the outer shell 3020extends over the outer lateral edge 3073 of the outer top lid 3070. Thetop edge 3023 of the outer shell 3020 is substantially flush with thetop surface 3071 of the outer top lid 3070. The inner and outer top lids3060, 3070 are welded to the inner and outer shells 3010, 3020respectively after the fuel is loaded into the cavity 3030. Conventionaledge groove welds can be used. However, it is preferred that allconnections between the components of the dual-walled DSC 3099 bethrough-thickness weld.

The dual-walled DSC 3099 also includes a first plate that acts as aninner base plate 3040 and a second plate that acts as an outer baseplate 3050. The inner and outer base plates 3040, 3050 are rigidplate-like structures having circular horizontal cross-sections. Theinvention is not so limited, however, and the shape and size of the baseplates 3040, 3050 is dependent upon the shape of the inner and outershells 3010, 3020. The inner base plate 3040 includes a top surface3041, a bottom surface 3042 and an outer lateral surface/edge 3043.Similarly, the outer base plate 3050 includes a top surface 3051, abottom surface 3052 and an outer lateral surface/edge 3053.

The top surface 3041 of the inner base plate 3040 forms the floor of thecavity 3030. The inner base plate 3040 rests atop the outer base plate3050. Similar to the other corresponding components of the dual-walledDSC 3099, the bottom surface 3042 of the inner base plate 3040 is insubstantially continuous surface contact with the top surface 3051 ofthe outer base plate 3050. As a result, the interface between the innerbase plate 3040 and the outer base plate 3050 is free of gaseousgaps/voids for thermal conduction optimization. An explosive joining, acladding process, a roller bonding process and/or a mechanicalcompression process can be used to effectuate the contact between thebase plates 3040, 3050. Preferably, the thickness of the inner baseplate 3040 is in the range of 50 mm to 150 mm. The thickness of theouter base plate 3050 is preferably in the range of 99 mm to 200 mm.Preferably, the length from the top surface of the outer top lid 3070 tothe bottom surface of the outer base plate 3050 is in the range of 4000mm to 5000 mm, but the invention is in no way limited to any specificdimensions.

The outer base plate 3050 may be equipped on its bottom surface with agrapple ring (not shown) for handling purposes. The thickness of thegrapple ring is preferably between 50 mm and 150 mm. The outer diameterof the grapple ring is preferably between 350 mm and 450 mm.

Referring now to FIGS. 36 and 38 concurrently, the inner shell 3010rests atop the inner base plate 3040 in a substantially uprightorientation. The bottom edge 3014 of the inner shell 3010 is connectedto the top surface 3041 of the inner base plate 3040 by athrough-thickness single groove (V or J shape) weld. The outer surface3012 of the inner shell 3010 is substantially flush with the outerlateral edge 3043 of the inner base plate 3040. The outer shell 3020,which circumferentially surrounds the inner shell 3010, extends over theouter lateral edges 3043, 3053 of the inner and outer base plates 3040,3050 so that the bottom edge 3024 of the outer shell 3020 issubstantially flush with the bottom surface 3052 of the outer base plate3050. The inner surface 3021 of the outer shell 3020 is also connectedto the outer base plate 3050 using a through-thickness edge weld. In analternative embodiment, the bottom edge 3024 of the outer shell 3020could rest atop the top surface 3051 of the outer base plate 3050(rather than extending over the outer later edge of the base plate3050). In that embodiment, the bottom edge 3024 of the outer shell 3020could be welded to the top surface 3051 of the outer base plate 3050.

When all of the seal welds discussed above are completed, thecombination of the inner shell 3010, the inner base plate 3040 and theinner top lid 3060 forms a first hermetically sealed structuresurrounding the cavity 3030, thereby creating a first pressure vessel.Similarly, the combination of the outer shell 3020, the outer base plate3050, and the outer top lid 3070 form a second sealed structure aboutthe first hermetically sealed structure, thereby creating a secondpressure vessel about the first pressure vessel and the cavity 3030.With the inclusion of the test port 3095, the seal of the secondpressure vessel also effectively includes the conduit, sealed at the endnot coupled to the test port. Theoretically, the first pressure vesselis located within the internal cavity of the second pressure vessel.Each pressure vessel is engineered to autonomously meet the stresslimits of the ASME Code with significant margins.

Unlike the prior art DSC, all of the SNF stored in the cavity 3030 ofthe dual-walled DSC 3099 share a common confinement space. The commonconfinement space (i.e., cavity 3030) is protected by two independentgas-tight pressure retention boundaries. Each of these boundaries canwithstand both sub-atmospheric supra-atmospheric pressures as needed,even when subjected to the thermal load given off by the SNF within thecavity 3030.

In the event of a failure of the first hermetically sealed structuresurrounding the cavity 3030, at least some of the backfilled helium willleak into the interstitial space 3097. Because helium is both an inertgas and a small molecule, the testing equipment and processes, describedin greater below, are able to draw helium through the interstitial space3097 for detection and determination of whether the first hermeticallysealed structure has failed.

A ventilated system 3101 is shown in FIGS. 39A & 39B. The cask lid 3107of a ventilated cask 3103 is shown in FIG. 39A, and a cross section ofthe ventilated cask 3103 is shown in FIG. 39B. As can be seen in FIG.39B, the ventilated cask 3103 includes a cylindrical cask body 3105 anda cask lid 3107. The cylindrical cask body 3105 includes a set of airinlet ducts 3109 near its bottom and a set of air outlet ducts 3111 nearits top. A dual-walled DSC 3099 containing decaying spent nuclear fuelstands upright inside the ventilated cask 3103, with a small diametricalclearance, in the form an annular gap 3113, being formed between aninner surface of the cylindrical cask body 3105 of the ventilated cask3103 and the outer surface 3115 of the DSC 399. The outer surface 3115of the DSC 3099 becomes heated due to the thermal energy being generatedby the spent nuclear fuel sealed in the DSC 3099. The heat of the outersurface 3115 causes the surrounding air column to heat and rise,resulting in a continuous natural convective ventilation action. Thecold air entering the air inlet ducts 3111 at the bottom of thecylindrical cask body 3105 is progressively heated as it rises in theannular gap 3113, reaching its maximum value as it exits the cylindricalcask body 3105. Different designs of such casks are known and describedin greater detail in the prior art, e.g., U.S. patent publication No.2003/0147486, published Aug. 7, 2003, and WO 2013/115881, published Aug.8, 2013, the disclosures of which are incorporated herein by referencein their entirety.

An assembled cask 3151 is shown in FIG. 40. The cask lid 3153 includesventilation ducts 3155, through one of which the conduit 3157 runs tothe outside of the cask 3151. The conduit 3157 extends down the side ofthe cask body 3159, and into an enclosure 3161 which is affixed to theexterior of the cask body 3159. Although not shown, the conduit may besecured to the cask body 3159 by appropriate brackets affixed to thecask body 3159. As an alternative, the conduit may extend away from thecask body entirely, to an enclosure that is affixed to an independentsupport (such as a nearby pole or other wall). The conduit 3157 ispreferably ¼ inch stainless steel conduit, as such conduit can beevacuated without collapsing. Other conduit materials and sizes thatexhibit a similar strength and properties as stainless steel conduit mayalso be used. Also, the conduit 3157 follows a tortuous path from thefirst end, where it is coupled to the test port, to the second end, towhich the seal, valve, and alternately the testing equipment arecoupled. The tortuous path is included so that there is no line of sightpath for radiation to escape from the DSC to the outside of the cask3151. Also, by running the conduit to the outside of the cask, thetesting described below may be performed while the cask remains in itsstorage position and the cask lid remains on the cask, therebyminimizing the amount of time needed to perform the test andsignificantly reducing the amount of radiation to which workers areexposed.

FIG. 41 shows a detailed view of the enclosure 3161 with a cover 3163 inplace, which serves to protect contents of the internal chamber of theenclosure 3161, and may be used to make the enclosure waterproof, ifdesired. One sidewall 3165 of the enclosure 3161 and cover 3163 mayinclude features for locking the cover in place—as shown these featuresare a pair of aligned rings 3167 on the sidewall 3165 and on the cover3163, which enable a lock or other security feature (e.g., a tag) to beplaced on the enclosure 3161.

The conduit 3157 passes through sidewall 3169 and into the internalchamber 3171 of the enclosure 3161, as shown in FIG. 42. Within theenclosure 3161, the second end 3173 of the conduit 3157 includes onetest apparatus connector 3175 and a secondary connector 3177. The twoconnectors 3175, 3177 provide a dual failsafe boundary in compliancewith ASME Code. When no test is being performed, a removable seal 3179is coupled to the test apparatus connector 3175. The removable seal 3179may be of any type suitable for sealing the test apparatus connector3175 and for use under the operating conditions described herein. Thetest apparatus connector 3175 is otherwise configured for coupling tothe test apparatus to be used, which may be a mass spectrometer leakdetector (MSLD) of the kind which are readily available on the markettoday, and one of ordinary skill in the art would be aware of the typesof different MSLDs available. The secondary connector 3177 is regulatedby a valve 3181 which is suitable for the operating conditions describedherein. During the testing process, once tests are performed by theMSLD, a source of a second inert gas (different from the inert gas whichis filled in the canister) may be connected to the secondary connectorso that the conduit and at least part of the interstitial space arebackfilled with this second inert gas.

An alternative for extending the conduit 3157 to the outside of the cask3151 is shown in FIG. 43. In this embodiment, a groove 3191 is formed inthe cask lid 3153, and the conduit 3157 is positioned in the groove3191, with the cask lid 3153 in place on the cask body 3159 so that theconduit 3157 may extend to the outside of the cask 3151. FIG. 44 showsthis same embodiment without the cask lid in place. As shown, theconduit 3157 extends across the top of the cask body 3159 from the testport 3193 formed in the outer top lid 3195 of the second pressurevessel. The conduit 3157 is coupled to the test port 3193 with anappropriate pressure fitting 3199, which may also be constructed fromstainless steel.

FIGS. 45 and 46 illustrate the test port 3193 in greater detail—in FIG.46, the cask is not shown for additional clarity. A portion of theinterstitial space 3201 exists between the inner top lid 3203 and theouter top lid 3195. As indicated above, although the interstitial space3201 may be very small, in such a small space, small, inert helium atomsmay still move around within such a space. In the event that largerinert atoms are used to fill the cavity of the canister, the choices ofhow to form the interstitial space may be more limited to take intoconsideration the presently disclosed system and method of leakdetection. The test port 3193 extends through the outer top lid 3195 sothat it is in fluidic communication with the interstitial space 3201.Thus, when the vacuum is created in the conduit, if helium molecules arepresent within the interstitial space, at least some of them will bedrawn into the conduit, and from there into the attached MSLD, so thatthey may be detected.

A block diagram showing the leak detection system and illustrating themethod for detecting leaks is depicted in FIG. 47. The interstitialspace 3251 is formed between the inner pressure vessel 3253 and theouter pressure vessel 3255. The first end 3257 of the conduit 3259 iscoupled to the test port 3261, and the second end 3263 of the conduit3259 is coupled to the leak detector 3265, so that the interstitialspace 3251, the test port 3261, the conduit 3259, and the leak detector3265 are all in fluidic communication. The leak detector 3265 includes avacuum system 3267, which is used to draw gas from the conduit 3259, andthus also from the interstitial space 3251, into the leak detector 3265for analysis. The leak detector also includes a gas sensor 3269, whichis preferably a mass spectrometer, and a pressure sensor 3271 to monitorthe state of the vacuum established in the conduit 3259. The gas sensor3269 is configured to detect the presence of the inert gas backfilledinto the cavity 3273 of the inner pressure vessel 3253.

During operation of the leak detector 3265, in one embodiment, the massspectrometer of an MSLD is used to analyze the gas being drawn from theinterstitial space while the vacuum is being established. An analysis isperformed to determine if the gas being drawn contains helium atoms, andthe number of helium atoms are counted. Depending upon the conditionsexisting at the time of testing, once the count of helium atoms passes apredetermined number, then a leak in the fluidic containment boundarythat is formed by the inner pressure vessel may be said to exist. Thispredetermined number may vary, depending upon the particular storagecontainer, conditions at the time the storage container wasmanufactured, or the conditions existing at the storage site. In otherwords, the presence of a single helium atom is not necessarilyindicative of a leak in the inner storage container. However, a count ofseveral helium atoms may be indicative of a leak. Further, because ofthe ease of the testing procedures, a particular canister might betested two or more times to confirm the presence of excess helium in theinterstitial space before a leak is determined to be positivelyidentified.

Also during operation of the leak detector 3265, in one embodiment, thepressure sensor of the MSLD is used to monitor the established vacuum inthe conduit and in the interstitial space. In the event that the vacuumdecreases over a short period of time from its initially establishedlevel, or alternatively if the MSLD needs to perform additional work tomaintain the vacuum once established, then a leak in the fluidiccontainment boundary that is formed by the outer pressure vessel may besaid to exist. In one embodiment, an MSLD is able to establish a vacuumin the conduit and in the interstitial space at about 10⁻⁸ atms, and ifthat established vacuum changes by about an order of magnitude, to about10⁻⁷ atms within a time period of about 1 second, then this is anindicator that there is a breach in the containment provided by theouter pressure vessel.

Once a test is complete, and whether or not a potential or actual leakis identified, the MSLD is decoupled from the conduit, and the removableseal may be put back in place on the test apparatus connector.Alternatively, before the removable seal is put back in place, theconduit may be backfilled with an inert gas that is different from theinert gas used to backfill the cavity of the inner pressure vessel.

The two tests performed by the leak tester are very accurate, and unlikecurrent testing systems, they do not require further investigation todetermine if the test resulted in a false positive identification of aleak.

The simplicity of the leak testing system and processes described aboveenables testing of radioactive materials containment on a regular basis,such as monthly, semi-annually, annually, or at any other choseninterval, without requiring dedicated (and costly) test equipment beingconnected to every individual containment system. Although dedicatedequipment permits constant monitoring, it has been found thatintermittent testing is sufficient and more cost effective. In addition,testing a single radioactive materials canister may be performedquickly, meaning that a reduction in manpower may be realized byimplementing such systems and methods. Finally, the additional equipmentthat is added to a canister for performing these leak tests is notcomplex and requires little maintenance, thereby enabling further costsavings to be realized.

V. Inventive Concept 5

With reference to FIGS. 48-52B, a fifth inventive concept will bedescribed.

The lid 4011 and top portion of a side wall 4013 for an MPC of the priorart are shown in FIG. 48. The top surface 4015 of the lid 4011 includesa beveled edge 4017, and the closure weld 4019 joining the lid 4011 tothe side wall 4013 is formed in the space between the half V-shapedspace between the beveled edge 4017 and the top portion of the side wall4013. As shown, the weld is a through-thickness single groove weldV-shaped groove, although the groove could instead be J-shaped. Due thephysical configuration of the lid, the sidewall, and the closure weld,this type of closure weld is not susceptible to 100% volumetricexamination.

A dual-walled MPC 4201 is illustrated in FIG. 49A, and this MPC 4201 isconfigured so that the closure weld may be subjected to 100% volumetricexamination. The dual-walled MPC 4201 may be used with any style of fuelbasket, such as the one described in U.S. Pat. No. 5,898,747, issuedApr. 27, 1999. In some instances it may be possible to use thedual-walled MPC 4201 without a fuel basket, depending on the intendedfunction. Furthermore, the dual-walled MPC 4201 may be used to storeand/or transport any type of high level radioactive materials and is notlimited to spent nuclear fuel.

As will become apparent from the structural description below, thedual-walled MPC 4201 creates two independent containment boundariesabout the storage cavity 4203 which operate to contain both fluidic (gasand liquid) and particulate radiological matter within the cavity 4203.As a result, if one containment boundary were to fail, the othercontainment boundary will remain intact. While theoretically the same,the containment boundaries formed by the dual-walled MPC 201 about thecavity 4203 can be literalized in many ways, including withoutlimitation a gas-tight containment boundary, a pressure vessel, ahermetic containment boundary, a radiological containment boundary, anda containment boundary for fluidic and particulate matter. These termsare used synonymously throughout this application. In one instance,these terms generally refer to a type of boundary that surrounds a spaceand prohibits all fluidic and particulate matter from escaping fromand/or entering into the space when subjected to the required operatingconditions, such as pressures, temperatures, etc.

Finally, while the dual-walled MPC 4201 is illustrated and described ina vertical orientation, it is to be understood that the dual-walled MPC4201 can be used to store and/or transport its load in any desiredorientation, including at an angle or horizontally. Thus, use of allrelative terms through this specification, including without limitation“top,” “bottom,” “inner” and “outer,” are used for convenience only andare not intended to be limiting of the invention in such a manner.

The dual-walled MPC 4201 includes a first shell that acts as an innershell 4205 and a second shell that acts as an outer shell 4207. Theinner and outer shells 4205, 4207 are preferably cylindrical tubes andare constructed of a metal. Of course, other shapes can be used ifdesired. The inner shell 4205 is a tubular hollow shell that includes aninner surface 4209, an outer surface 4210, a top edge 4212 and a bottomedge 4215. The inner surface 4209 of the inner shell 4205 forms acavity/space 4203 for receiving and storing SNF. The cavity 4203 is acylindrical cavity formed about a central axis.

The outer shell 4207 is also a tubular hollow shell that includes aninner surface 4221, an outer surface 4223, a top edge 4225 and a bottomedge 4227. The outer shell 4207 circumferentially surrounds the innershell 4205. The inner shell 4205 and the outer shell 4207 areconstructed so that the inner surface 4221 of the outer shell 4207 is insubstantially continuous surface contact with the outer surface 4223 ofthe inner shell 4205. In other words, the interface between the innershell 4205 and the outer shell 4207 is substantially free of gaps/voidssuch that the two shells 4205, 4207 are in conformal contact. This canbe achieved through an explosive joining, a cladding process, a rollerbonding process and/or a mechanical compression process that bonds theinner shell 4205 to the outer shell 4207. The continuous surface contactat the interface between the inner shell 4205 and the outer shell 4207reduces the resistance to the transmission of heat through the inner andouter shells 4205, 4207 to a negligible value. Thus, heat emanating fromthe spent nuclear fuel loaded within the cavity 4203 can efficiently andeffectively be conducted outward through the shells 4205, 4207 where itis removed from the outer surface 4223 of the outer shell viaconvection.

The inner and outer shells 4205, 4207 are preferably both made of ametal. As used herein, the term metal refers to both pure metals andmetal alloys. Suitable metals include without limitation austeniticstainless steel and other alloys including Hastelloy™ and Inconel™. Ofcourse, other materials can be utilized. The thickness of each of theinner and outer shells 4205, 4207 is preferably in the range of 5 mm to25 mm. The outer diameter of the outer shell 4207 is preferably in therange of 1700 mm to 2000 mm. The inner diameter of the inner shell 4205is preferably in the range of 1700 mm to 1900 mm. The specific sizeand/or thickness of the shells 4205, 4207, however, is a matter ofdesign choice.

In some embodiments, it may be further preferable that the inner shell4205 be constructed of a metal that has a coefficient of thermalexpansion that is equal to or greater than the coefficient of thermalexpansion of the metal of which the outer shell 4207 is constructed.Thus, when the spent nuclear fuel that is stored in the cavity 4203emits heat, the outer shell 4207 will not expand away from the innershell 4205. This ensures that the continuous surface contact between theouter surface 4210 of the inner shell 4205 and the outer surface 4223 ofthe outer she114 207 will be maintained and a gaps will not form underheat loading conditions.

The dual-walled MPC 4201 also includes a first top plate that acts as aninner top lid 4229 for the inner shell 4205 and a second top plate thatacts as an outer top lid 4231 for the outer shell 4207. The inner andouter top lids 4229, 4231 are plate-like structures that are preferablyconstructed of the same materials discussed above with respect to theshells 4205, 4207. Preferably the thickness of the inner top lid 4229 isin the range of 99 mm to 300 mm. The thickness of the outer top lid 4231is preferably in the range of 50 mm to 150 mm. The invention is not,however, limited to any specific dimensions, which will be dictated on acase-by-case basis and the radioactive levels of the spent nuclear fuelto be stored in the cavity 4203.

The inner top lid 4229 includes a top surface 4233 with a beveled edge4235, a bottom surface 4237, an outer lateral surface/edge 4239, and achannel 4241 formed in the top surface 4233 and set in from the bevelededge 4235. The outer top lid 4231 includes a top surface 4243 with abeveled edge 4245, a bottom surface 4247, an outer lateral surface/edge4249, and a channel 4251 formed in the top surface 4243 and set in fromthe beveled edge 4245. When fully assembled, the outer lid 4231 ispositioned atop the inner lid 4229 so that the bottom surface 4247 ofthe outer lid 4231 is in substantially continuous surface contact withthe top surface 4233 of the inner lid 4229. Both the inner top lid 4229and the outer top lid 4231 also include vent and/or drain ports 4253,4255.

During loading procedure involving spent nuclear fuel, the cavity 4203is loaded with the spent nuclear fuel, then the inner top lid 4229 ispositioned so as to enclose the top end of the cavity 4203 and restsatop brackets (not shown). Once the inner top lid 4229 is in place, aclosure weld is formed to seal the inner top lid 4229 to the inner shell4205. The top lid 4229 may be welded to the inner shell 4205 using anysuitable welding technique or combinations of techniques that use afiller material. Examples of suitable welding techniques includeresistance seam welding, manual metal arc welding, metal inert gaswelding, tungsten inert gas welding, submerged arc welding, plasma arcwelding, gas welding, electroslag welding, thermit welding.

After the cavity 4203 is sealed by the closure weld, it may then beevacuated/dried via the appropriate method and backfilled with nitrogen,helium or another inert gas using the ports 4249 of the inner lid 4229that form passageways into the cavity 4203. The ports 4249 maythereafter be filled with a metal or other wise plugged so as tohermetically seal the cavity 4203.

The outer shell 4207 has an axial length that is greater than the axiallength of the inner shell 4205. As such, the top edge 4225 of the outershell 4207 extends beyond the top edge 4211 of the inner shell 4205.Similarly, the bottom edge 4227 of the outer shell 4207 extends beyondthe bottom edge 4215 of the inner shell 4205.

The offset between the top edges 4211, 4225 of the shells 4205, 4207allows the top edge 4211 of the inner shell 4205 to act as a ledge forreceiving and supporting the outer top lid 4231. When the inner top lid4229 is in place, the inner surface 4209 of the inner shell 4205 extendsover the outer lateral edges 4239. When the outer top lid 4231 is thenpositioned atop the inner lid 4229, the inner surface 4221 of the outershell 4207 extends over the outer lateral edge 4249 of the outer top lid4231. The top edge 4225 of the outer shell 4207 is substantially flushwith the top surface 4253 of the outer top lid 4231. The inner and outertop lids 4229, 4231 are welded to the inner and outer shells 4205, 4207respectively after the fuel is loaded into the cavity 4203. Similar tothe inner top lid 4229, once the outer top lid 4231 is in place, aclosure weld is formed to seal the outer top lid 4231 to the outer shell4207. The outer top lid 4231 may be welded to the outer shell 4207 usingany suitable welding technique or combinations of techniques that use afiller material. Examples of suitable welding techniques includeresistance seam welding, manual metal arc welding, metal inert gaswelding, tungsten inert gas welding, submerged arc welding, plasma arcwelding, gas welding, electroslag welding, thermit welding. The closurewelds sealing the inner and outer top lids 4229, 4231 to the inner andouter shells 4205, 4207 may be subjected to 100% volumetric examinationonce the welds are formed. It is to be understood that the closure weldfor the inner top lid 4229 is to undergo volumetric examination beforethe outer top lid 4231 put in place.

The dual-walled MPC 4201 also includes a first plate that acts as aninner base plate 4265 and a second plate that acts as an outer baseplate 4267. The inner and outer base plates 4265, 4267 are rigidplate-like structures having circular horizontal cross-sections. Theinvention is not so limited, however, and the shape and size of the baseplates is dependent upon the shape of the inner and outer shells. Theinner base plate 4265 includes a top surface 4269, a bottom surface 4271and an outer lateral surface/edge 4273. Similarly, the outer base plate4267 includes a top surface 4275, a bottom surface 4277 and an outerlateral surface/edge 4279.

The top surface 4269 of the inner base plate 4265 forms the floor of thecavity 4203. The inner base plate 4265 rests atop the outer base plate4267. Similar to the other corresponding components of the dual-walledMPC 201, the bottom surface 4271 of the inner base plate 4265 is insubstantially continuous surface contact with the top surface 4275 ofthe outer base plate 4267. As a result, the interface between the innerbase plate 4265 and the outer base plate 4267 is free of gaseousgaps/voids for thermal conduction optimization. An explosive joining, acladding process, a roller bonding process and/or a mechanicalcompression process can be used to effectuate the contact between thebase plates 4265, 4267. Preferably, the thickness of the inner baseplate 4265 is in the range of 50 mm to 150 mm. The thickness of theouter base plate 4267 is preferably in the range of 99 mm to 200 mm.Preferably, the length from the top surface of the outer top lid 4231 tothe bottom surface of the outer base plate 4267 is in the range of 4000mm to 5000 mm, but the invention is in no way limited to any specificdimensions.

The outer base plate 4267 may be equipped on its bottom surface with agrapple ring (not shown) for handling purposes. The thickness of thegrapple ring is preferably between 50 mm and 150 mm. The outer diameterof the grapple ring is preferably between 350 mm and 450 mm.

The inner shell 4205 rests atop the inner base plate 4265 in asubstantially upright orientation. The bottom edge 4215 of the innershell 4205 is connected to the top surface 4275 of the inner base plate4265 by a through-thickness single groove (V or J shape) weld. The outersurface 4210 of the inner shell 4205 is substantially flush with theouter lateral edge 4273 of the inner base plate 4265. The outer shell4207, which circumferentially surrounds the inner shell 4205, extendsover the outer lateral edges 4273, 4279 of the inner and outer baseplates 4265, 4267 so that the bottom edge 4227 of the outer shell 4207is substantially flush with the bottom surface 4277 of the outer baseplate 4267. The inner surface 4221 of the outer shell 4207 is alsoconnected to the outer base plate 4267 using a through-thickness edgeweld. In an alternative embodiment, the bottom edge 4227 of the outershell 4207 could rest atop the top surface 4275 of the outer base plate4267 (rather than extending over the outer later edge of the base plate4267). In such an embodiment, the bottom edge 4227 of the outer shell4207 could be welded to the top surface 4275 of the outer base plate4267.

When all of the seal and closure welds discussed above are completed,the combination of the inner shell 4205, the inner base plate 4265 andthe inner top lid 4229 forms a first hermetically sealed structuresurrounding the cavity 4203, thereby creating a first pressure vessel.Similarly, the combination of the outer shell 4207, the outer base plate4267, and the outer top lid 4231 form a second sealed structure aboutthe first hermetically sealed structure, thereby creating a secondpressure vessel about the first pressure vessel and the cavity 4203.Theoretically, the first pressure vessel is located within the internalcavity of the second pressure vessel. Each pressure vessel is engineeredto autonomously meet the stress limits of the ASME Code with significantmargins.

FIG. 49B illustrates a single-walled MPC 4285 which is constructed in asimilar manner as each pressure vessel of the double-walled MPC 4201discussed above. This single-walled MPC 4287 includes a side wall 4289seal welded to a base plate 4291, and a top plate 4293. The top surface4295 of the top plate 4293 includes a beveled top edge 4297 and achannel 4299 set in from the top edge 4297. Having the lid configuredwith the channel 4299 makes it so that the closure weld may be subjectedto 100% volumetric examination. All other parts of the single-walled MPC285 may be constructed in the same manner described above.

A detailed view a top plate 4311 and the closure weld 4313 sealing thetop plate 4311 to a side wall 4315 of an MPC are illustrated in FIG.49C. The channel 4317 in the top surface 4319 is set in from the beveledtop edge 4321. The channel 4317 extends below the top surface 4319 atleast as much as does the bevel of the beveled top edge 4321. In someembodiments, depending upon the configuration of the probe being used,it may be desirable to have the channel 4317 extend deeper below the topsurface than the bevel in order to accommodate the probe. The channel4317 is sufficiently wide so that a probe used for examining the closureweld may be placed within the channel 4317 and moved circumferentiallyaround the top plate 4311 for purposes of achieving 100% volumetricexamination of the closure weld. For some types of probes, the channelmay be as wide as 2″ to 3″, although these dimensions may varysignificantly to accommodate the configuration of the probe used toexamine the closure weld. The side wall 4323 of the channel 4317 nearestthe beveled top edge 4321 is placed at an angle that is approximatelyparallel to the angle of the beveled top edge 4321. However, in someembodiments the angle of this channel side wall may vary from the angleof the top beveled edge by 5°-20° or more, depending upon theconfiguration of probe being used. The side wall 4323, however, may beformed at any angle relative to the beveled top edge 4321. The oppositewall 4325 of the channel 4317 may have any configuration, from awell-defined wall, as is shown, to a curved or flat surface adjoiningthe bottom 4327 of the channel 4317.

One embodiment of a top plate 4331 is shown in FIG. 50 with ports 4333positioned in the central portion 4335 of the top surface 4337 of thetop plate 4331, radially inward from the channel 4339. The ports 4333may serve any desired purpose for the MPC for which the top plate 4331is used, and the different ports may be used for different purposes.Examples of purposes for the ports include their use as vent ports, asvacuum ports, as drain ports, as backfill ports, as test ports, amongothers. Another embodiment of a top plate 4341 is shown in FIG. 51. Inthis embodiment, the ports 4343 are positioned within the channel 4345.In other embodiments, ports may be positioned both within the channeland in the central portion of the top surface of the top plate.

FIGS. 52A and 52B illustrate the process of performing the 100%volumetric examination of the closure weld after it has been formed.With the top plate in place on the top opening of the sidewall, the topplate having a channel as described above, the closure weld may beformed by automated equipment, such as is well known in the art. Inorder to volumetrically examine the closure weld, probes are mounted ona support arm capable of rotating and positioning the probes to performthe volumetric examination of the closure weld. For example, the probesmay be mounted on the same type of weld arm that is used in theautomated process for forming the closure weld. The volumetricexamination may be carried out once the entire weld is formed.

Only the end of the support arm 4371 is illustrated in FIG. 52A tosimplify the drawing. It is to be understood that the support arm mayhave any appropriate configuration that is capable of supporting theprobes and moving them around the top plate to perform the volumetricexamination, as many different types and configurations of such supportarms are well-known in the arts, including combinationrotary/articulating robotic arms. Two probes 4373, 4375 are affixed tothe end of the support arm 4371, and the support arm is configured forautomated or remote positioning of the probes so that the volumetricexamination of the closure weld may be performed. The first probe 4373is positioned on the outside of the top of the side wall 4377, and thesecond probe 4375 is shown just prior to being positioned within thechannel 4379 formed in the top surface 4381 of the top plate 4383. Thissecond probe 4375 is shown positioned within the channel 4379 in FIG.52B. Once the two probes are in position, the entire volume of a portionof the closure weld is disposed between the two probes, and that entirevolume may be volumetrically examined. By activating the two probes andmoving them synchronously around the top plate, maintaining theirrelative position with respect to the closure weld, the entirety of theweld is passed between the two probes in one circumscription of the topplate. It is therefore possible, with the appropriate examinationtechnology, to perform a 100% volumetric examination of the closureweld. Using well-known processes associated with the selectedexamination technology, the integrity of the entire closure weld may bedetermined from the examination.

In the embodiment of FIG. 52A, the entire closure weld is formed first,followed by the volumetric examination of the closure weld. In theembodiment of FIG. 52B, the weld head 4385 extends from the same supportarm (not shown in FIG. 52B) as the probes 4373, 4375. The weld arm thenmoves the weld head around the top edge of the top plate to form theclosure weld, and the probes trail the weld head to perform thevolumetric examination. This embodiment may be used to form the weld andsubstantially concurrently volumetrically examine the weld. For amulti-pass closure weld, having the probes trail the weld head in thismanner enables a separate volumetric examination of each pass of theclosure weld. Due to the heat generated from the welding process, whichmay interfere with the examination process, this embodiment may be bestsuited for use in pools or in the presence of a coolant, such as a flowof demineralized water

In certain embodiments, a Linear Scan-Phased Array UT system may be usedto examine the closure weld, and for such embodiments the probes areultrasound transducer probes. Such a UT system is capable of conductingthe 100% volumetric examination of the closure weld within a matter ofminutes. Beneficially, with the top plate configured as described aboveand with use of the two probes, no human activity needs to be directlyinvolved for placing the top plate, forming the closure weld, orexamining the integrity of the closure weld, so that work crews are notexposed to any significant doses of radiation.

In embodiments where a UT system is used outside of a pool of water orother fluid, a coupling agent, such as demineralized water or anappropriate gel, may be introduced between the transducer probes and thetop plate and/or side wall to increase the amount of ultrasound energythat passes into the closure weld, thereby improving the volumetricexamination. As is well known in the art of UT, only small amounts ofthe coupling agent are needed to form a thin film, minimizing air gaps,between the transducer probe and the parts of the MPC into which theultrasound energy is being directed. Therefore, a simple drip systemsuffices to introduce a coupling agent such as demineralized water tothe process of volumetric examination described herein.

In embodiments involving a high heat load canister, to ensure that themetal temperature of the weld mass is not too high for an accurate UTreading, it may be necessary to circulate cooling water through the MPCusing the vent and drain ports in the lid before performing thevolumetric examination. As an alternative, the use of a coupling agentfor ultrasound energy, such as demineralized water, between thetransducer probes and the MPC helps to insure that the volumetricexamination is performed at a uniform temperature, thereby preservingthe UT calibration integrity.

VI. Inventive Concept 6

With reference to FIGS. 53-59, a sixth inventive concept will bedescribed.

FIG. 53 illustrates an apparatus for transferring spent nuclear fuel inthe form of a transfer cask 5011. The transfer cask 5011 includes acylindrical inner shell 5013 which forms a cavity 5015 along with thetop lid 5017 and the bottom lid 5019. As shown, a canister 5021 forholding spent nuclear fuel is disposed within the cavity 5015. The innershell 5013 has a longitudinal axis 5023, and the inner shell 5013 has aslightly larger radius, measured from the longitudinal axis 5023, ascompared to the canister 5021, to create an annulus 5025 of spacebetween the inner shell 5013 and the canister 5021 disposed in thecavity 5015. This annulus 5025, as discussed in greater detail below,serves to enable cooling of the canister 5021 by ventilation withatmosphere.

The transfer cask further includes an intermediate shell 5027 and anouter shell 5029. Each of the inner shell 5013, the intermediate shell5027, and the outer shell 5029 are preferably made from carbon steel,with the top of each welded to a top flange 5031, and the bottom of eachwelded to a bottom flange 5033. The intermediate shell 5027 is disposedconcentrically around and spaced apart from the inner shell 5013,thereby forming a second annulus 5035. This second annulus 5035 iscapable of holding a gamma absorbing material such as concrete, lead, orsteel. Lead is preferred because it most effectively provides gammashielding for the radioactive spent nuclear fuel once it is placedwithin cavity 5015. The outer shell 5029 is disposed concentricallyaround and spaced apart from the intermediate shell 5027, therebyforming a third annulus 5037. This third annulus 5037 is capable ofholding a neutron absorbing material such as water or the aforementionedaluminum trihydrate-boron carbide-epoxy mixture. As shown, the thirdannulus 5037 includes panels of a metal matrix composite. Foralternative embodiments in which water is to be used in the thirdannulus, U.S. Pat. No. 7,330,525 describes a manner in which the outershell may be formed, in order to contain water, and a process for usingwater as a neutron absorber in the transfer cask during transfer of acanister containing spent nuclear fuel.

The top lid 5017 is securable to the top flange 5031 by extending bolts(not shown) through the top lid 5017 to engage the top flange 5031. Thetop lid 5017 is typically only secured to the top flange 5031 once thecanister 5021 is in place within the cavity 5015 during the transferprocess. A central opening 5039 in the top lid 5017 provides access tothe canister 5021 for performing certain handling operations withrespect to the canister 5021 while the top lid 5017 is secured to topflange 5031.

Referring to FIG. 54A, the top flange 5031 is integrally formed throughforging and machining so that it does not include any joints, welds, orseams, and so that it does not include parts that are separately formedand then subsequently joined together. The top flange 5031 is machinedto include two trunnions 5041 to be used for lifting the transfer caskwith a crane. As shown in FIGS. 54A-54C, the trunnions may be of avariety of cross sections such as round trunnions 5041 (FIG. 54A),rectangular trunnions 5041 b (FIG. 54B), obround trunnions 5041 c (FIG.54C), oblong trunnions, and the like. The cross-sectional form of thetrunnions may be any shape according to design choice, with specificimplementations limited only by the equipment used to hoist the transfercask.

More than two trunnions may be machined as part of the top flange, basedupon design choices and the lifting system with which the transfer caskis to be used. For purposes of stability during lifting, the trunnionsare distributed approximately equidistantly around the top flange.

The top flange 5031 also includes a seating groove 5043 for a sealingring (not shown), which serves as a seal, against the canister andwithin the annulus, when the canister is placed in the cavity. Aplurality of ventilation channels 5045 are included in the top flange5031, with internal channel inlets 5047 on the interior surface 5049 ofthe top flange 5031 located below the seating 5043 so that when acanister is placed, air is directed through the ventilation channels5045. The ventilation channels 5045 open up to the exterior of the topflange 5031, and to the exterior of the transfer cask, at externalchannel outlets 5051 so that the ventilation channels fluidicallyconnect the annulus 5025 with the exterior of the top flange 5031 andthe transfer cask. The ventilation channels 5045 through the top flange5031 may have a variety of forms or paths, however, because air is beingused to ventilate the transfer cask, and unlike water, air is not a goodneutron absorber, the one design constraint for the ventilation channelsis that the paths of the ventilation channels preclude a direct line oftravel from within the cavity to the exterior of the top flange. Withthis design constraint on the ventilation channels of the top flange,emissions from the canister cannot pass through an all-air pathway fromthe canister to the exterior of the transfer cask.

The integral design of the trunnions 5041 as part of the top flange 5031serves to eliminate joints between the top flange and the trunnions,thereby significantly improving the fidelity of structural integrity ofthe overall lifting system (as compared to the prior art, in which thetrunnions are joined to the top flange by welding or a threaded joint).The top flange 5031 is also enlarged as compared to top flanges of theprior art, but still keeping within the constraints of the size of thecask pit in the pool and the lifting limit of the cask crane. Eventhough enlarged, the top flange 5031, inclusive of the integraltrunnions 5041, has a smaller outer diameter as compared to the outershell 5029. To aid in preventing damage that may be caused by protrudingtrunnions in the event of a transfer cask accidentally tipping intoother casks, each trunnion 5041 is disposed within a recess 5053 of thetop flange 5031. The larger top flange 5031 also serves to provideincreased shielding in the top region of the cask where most humanactivity (to weld and dry the canister) occurs.

Turning back to FIG. 53, the bottom lid 5019 is secured to the bottomflange 5033 by a plurality of bolts (not shown) that extend throughholes in the bottom flange 5033 the engage the bottom lid 5019. Thebottom lid 5019 includes an impact zone 5061 positioned directly beneaththe cavity 5015. The bottom lid 5019 also includes a gamma-absorbinglayer 5063, such as lead, below the impact zone 5061. To be mosteffective in absorbing impacts from accidental falls of the transfercask, the impact zone 5061 extends substantially under the entirety ofthe cavity 5015. The impact zone includes an impact absorbing structure5065 which can serve to cushion the fall of a canister loaded into thetransfer cask, thereby providing some damage protection to the fuel inthe event of a handling mishap while the transfer cask is being movedaround the building or plant site. As shown, the impact absorbingstructure 5065 is formed by a plurality of cylindrical tubes 5067 withinthe bottom lid 5019. These tubes 5067 are distributed throughout theimpact zone 5061, with their longitudinal axes aligned with a majordimension (i.e., the diameter) of the bottom lid 5019. The thickness,number of tubes, and the cross-sectional shape of the tubes are a matterof design choice based upon the particular implementation. Factors thatmay be taken into consideration for these design choices includeestimated drop height (based on the operational procedures of thefacility), the weight of the canister, and the weight of the loadedtransfer cask.

Computations have shown that a set of parallel 2-inch tubes distributedthroughout the impact zone 5061 can limit the impact load experienced bya 40-ton canister, placed with a transfer cask, falling from 18 inchesonto a concrete pad to a g-force of less than 25 (in the absence of theimpact limiter, the g-force may shoot up to over 100).

A plurality of ventilation channels 5071 are included in the bottom lid5029, with external channel inlets 5073 on the external surface 5075 ofthe bottom lid and internal channel outlets 5077 located so that theventilation channels 5071 can direct an air flow into the annulus 5025.A plurality of ventilation channels configured in this manner are formedapproximately equidistantly around the bottom lid to provide coolingventilation to the canister 5021 outside of the storage pool. At thepoint of intersection between the channel outlets 5077 and the annulus5025, the bottom flange 5033 is configured with a chamfered surface 5079to broaden out the annulus 5025, thereby providing an enlarged spaceabout the base of the canister 5021 into which air may be drawn throughthe ventilation channels 5071. Each channel inlet 5073 is configured toreceive a sealing plug (not shown), which may threadably engage thechannel inlet 5073 to provide a seal and turn the ventilation channeland annulus into a “blind” cavity that does not have ingress through thebottom lid. Similar plugs may be placed in the channel outlets of thetop flange, thereby rendering the entire annuls cavity into a “blind”cavity. Such plugs may be placed under circumstances where it isdesirable to protect the ventilation channel from ingress ofcontaminated water or other matter, either solely at the bottom of thetransfer cask, or at the top and the bottom.

A second example of a ventilation channel 5081 is shown in FIG. 57, anda plurality of ventilation channels 5081 configured in this manner areformed approximately equidistantly around the bottom lid to providecooling ventilation to the canister 5021 outside of the storage pool.Again, at the point of intersection between the channel outlets 5083 andthe annulus 5025, an enlarged space 5085 is included about the base ofthe canister 5021 into which air may be drawn through the ventilationchannels 5081. The channel inlets 5087 may also be configured to receivea sealing plug (not shown).

The ventilation channels 5071 through the bottom lid 5029 may have avariety of forms or paths, however, because air is being used toventilate the transfer cask, and unlike water, air is not a good neutronabsorber, the one design constraint for the ventilation channels is thatthe paths of the ventilation channels preclude a direct line of travelfrom within the cavity to the exterior of the bottom lid. With thisdesign constraint on the ventilation channels of the bottom lid,emissions from the canister cannot pass through an all-air pathway fromthe canister to the exterior of the transfer cask.

FIGS. 56 and 57 illustrate another alternative embodiment of the bottomlid 5091 and an integrated ventilation channel. In this embodiment, theventilation channel is a toroidal-shaped distribution channel 5093having a single channel inlet 5095 and a plurality of channel outlets5097 which are positioned to fluidically connect the annulus, formedbetween the inner shell of the transfer cask and the canister placed inthe cavity, with the exterior of the bottom lid 5091 and the transfercask. The radial position of the channel inlet 5095 is different thanthe radial position of the channel outlets 5097 so that theconfiguration of the ventilation channel 5093 precludes a direct line oftravel from within the cavity to the exterior of the bottom lid.

A transfer cask which includes the annulus between the inner shell andthe canister, the ventilation channels in the top flange, and theventilation channels in the bottom flange, configured in any of themanners discussed above, when out of a storage pool allows ambient airto ventilate up the annulus to enhance the heat removal efficacy of thecask. Calculations have shown that a mere ¾ inch wide annulus can reducethe fuel cladding temperature by as much as an additional 20° C., incomparison to a blind annulus with stagnant air (which is thestate-of-the-art). And, as compared to a water-cooled annulus, a passiveambient air-cooled annulus is much simpler, easier to use, and easier tomaintain, thereby resulting in greater operational reliability.

Such a transfer cask will remove decay heat from the canister byventilation action. For low heat canisters (those generating less thanabout 18 kW), the natural ventilation through the annulus coupled withheat dissipation from the external surfaces of the cask are sufficientto keep the contents of the canister from overheating.

In circumstances where additional cooling is needed for higher heat loadcanisters, beyond the cooling that can be provided by ventilation ofambient air, chilled air can be forced through the annulus. One suchsystem is shown schematically in FIG. 58. And, even a forced air systemis simpler and easier to use and maintain than a cooled water system. Aforced air system is most easily used when the bottom lid includes anintegrated ventilation channel with a single channel inlet, such as isshown in FIG. 56. During use, an air compressor 5111 operates to storecompressed air in a compressed air tank 5113, and the air outlet 5115 ofthe compressed air tank 5113 is fluidically coupled though anappropriate air line 5117 to the channel inlet 5119 of the bottom lid ofthe transfer cask 5121. The compressed air tank 5113 itself may becooled by ambient air, or it may be cooled by an active cooling orrefrigeration system 5123. As those of skill in the art will recognize,decompression of air naturally decreases the temperature of that air, sothat the amount of cooling needed for the compressed air tank 5113 willdepend upon the heat dissipation needs of the transfer cask. Forexample, a refrigeration system may be used to cool the compressed airtank to a temperature as low as 5° C., thereby causing the decompressedair from the compressed air tank to be cooler still when it is directedinto the annulus of the transfer cask. The decompressed air is deliveredinto the ventilation channel of the bottom lid, and then into theannulus, by the positive pressure of expansion upon release from thecompressed air tank.

The air compressor and compressed air tank are sized to provide thecooled air at a sufficiently high velocity to ensure turbulent flowconditions within the annulus. Calculations have shown that a 50 HPcompressor is adequate to cool a canister with as much as 35 kW heatload. The chilled air is heated within the annulus and exits thetransfer cask through the ventilation channels in the flange.

As an alternative to using a compressed air tank and an air compressor,chilled air may alternatively be forced into the annulus by use of ablower.

The advantages of a forced air cooling system include greatersimplicity, as compared to a water cooled system, use of single phasecooling medium (air rather than water) and mitigation of the concerns ofleakage (no water spillage) at the flanged or screwed joints. Theperformance of the system is easily monitored by measuring thetemperature of the exiting heated air from the cask

FIG. 59 is a flowchart showing the process of moving a transfer cask, asdescribed above with ventilation channels, loaded with a canister from apool for transport or storage of the canister.

The process starts 5121 with a fully loaded canister in the cavity oftransfer cask without the top lid in place. The process of loading thecanister is well-known to those of skill in the art, and so they are notdiscussed herein. As the transfer cask sits in the pool, one or moreplugs may be in place in the bottom lid to seal off the ventilationchannels to make the ventilation channels and the annulus a “blind”cavity, thereby protecting from ingress of contaminated water. Withoutthe plugs in place, water fills the annulus and helps to remove heatgenerated by the spent nuclear fuel in the canister.

The hoist of a crane is lowered into the pool and secured to thetrunnions of the transfer cask. Once the hoist is secured to thetrunnions, the crane lifts 5123 the transfer cask, along with thecanister payload, out of the storage pool. The transfer cask is designedso that at this stage in the process, the combined weight of thetransfer cask and payload is equal to or less than the rated liftingcapacity of the crane.

Once lifted out of the storage pool, the crane sets transfer cask down5125 in a staging area. At this point, the canister contains pool waterin addition to the spent nuclear fuel. This pool water acts as a neutronabsorber as long as it is in the canister, and it removed from thecanister in order to store the spent nuclear fuel in a dry-state. In theevent that one or more plugs are in place in the bottom lid, they areremoved 5127 to allow ventilated cooling by circulation of atmosphericair through the annulus.

As an alternative, at this point, a compressed air tank is fluidicallycoupled to the channel inlet of the bottom lid using an appropriate hoseand coupling. The compressed air tank is coupled to an air compressor sothat compressed air is maintained in the tank during use. Compressed airfrom the tank is decompressed and passed into the channel inlet duringthe remaining steps of moving the transfer cask while it is loaded withthe canister.

Once the transfer cask is ventilated, the pool water in the canister ispumped out 5129, and the spent nuclear fuel in the canister is allowedto dry. The canister is then backfilled with an inert gas, such ashelium, and sealed. The cask lid is then secured 5131 to transfer cask.The transfer cask is then lifted by the crane and moved to a positionabove another cask 5133, at which point the bottom lid is removed andthe canister is lowered into the other cask 5135. The other cask may bea storage cask, if the spent nuclear fuel is to be stored long-term, orit may be a transport cask suitable for moving spent nuclear fuel overlong distances.

Once the canister is removed from the transfer cask, the transfer caskmay be reused to perform the above described procedure again. To reusethe transfer cask, the one or more plugs are again put in place in thebottom lid to seal off the ventilation channels.

VI. Inventive Concept 7

With reference to FIGS. 60-66, a seventh inventive concept will bedescribed.

Referring to FIG. 60, a prior art ventilated system 1 is shown. Theprior art ventilated system 1 comprises ventilated cask 10 thatcomprises a cylindrical cask body 11 and a cask lid 12. The cylindricalcask body 11 comprises a set of air inlet ducts 13 near its bottom and aset of air outlet ducts 14 near its top. A dry storage canister 20containing decaying spent nuclear fuel stands upright inside the VVO 10with a small diametral clearance, in the form an annular gap 15, beingformed between an inner surface of the cylindrical cask body 12 of theVVO 10 and the outer surface 21 of the canister 20. The outer surface 21of the canister 20 becomes heated due to the thermal energy beinggenerated by the spent nuclear fuel sealed in the canister 20. The heatouter surface 21 causes the surrounding air column to heat and rise,resulting in a continuous natural convective ventilation action. Thecold air entering the air inlet ducts 14 at the bottom of thecylindrical cask body 12 is progressively heated as it rises in theannular gap 15, reaching its maximum value as it exits the cylindricalcask body 12.

The metal temperature of the canister 20 (which is typically made ofaustenitic stainless steel) likewise increases with increasing height(i.e., vertical distance from the bottom of the canister 20), morerapidly in the bottom half of the canister 20 where the ΔT between theair temperature and the canister temperature is larger than the top halfwhere the ΔT between the air temperature and the canister temperature isless. A larger ΔT draws results in the heat of the canister 20 beingdrawn out and away more vigorously. Referring to FIGS. 2 and 3, typicalair and canister temperatures, as a function of canister height, aregraphed for the prior art ventilated system 1 @ a 28.74 kW heat load (ofthe spent nuclear fuel) and a 26.6° C. temperature for the ambientcooling air using an axisymmetric model in the computer code FLUENT. AsFIG. 3 shows, the surface temperature of the canister is within 90° C.of the ambient air temperature at a reference of 26.6° C. forapproximately 10.4% of its height.

The region where the canister surface temperature is within the range of90° C. above the ambient temperature has been identified by research asa potential “vulnerable zone” to SCC, especially in marine environments.This is particularly true of weld seams and heat affected zones in thecanister's confinement boundary. Thus, weld seams in canisters of ISFSIslocated at coastal sites, i.e., those on the Atlantic and Pacificcoasts, are especially vulnerable to SCC. Moreover, as the spent nuclearfuel decays with the passage of time, the emitted heat generation ratedrops as well, which puts more and more of the canister surface in the“vulnerable zone” (i.e., within 90° C. of the ambient air temperature).This potential degradation of the canister's confinement boundary isinconsistent with the evolving policy to extend the service life ofISFSIs by many decades.

Referring now to FIGS. 63-66 concurrently, a ventilated storage system61000 according to an embodiment of the present invention isillustrated. The ventilated storage system 61000 is a vertical,ventilated, dry, SNF storage overpack that is fully compatible with 1000ton and 125 ton transfer casks for spent fuel canister transferoperations. The ventilated cask 50 can, of course, be modified and/ordesigned to be compatible with any size or style of transfer cask.Moreover, while the ventilated storage system 61000 is discussed hereinas being used to store SNF, it is to be understood that the invention isnot so limited and that, in certain circumstances, the ventilatedstorage system 61000 can be used to store other forms of radioactivewaste that is emitting a heat load, such as any high level radioactivewaste.

The ventilated storage system 61000 generally comprises a hermeticallysealed metal canister 6200 and a ventilated cask 6600. The canister 6200forms a fluidic containment boundary about the SNF loaded therein. Thus,the canister 6200 can be considered a hermetically sealed pressurevessel. The canister 6200, however, is thermally conductive so that heatgenerated by the SNF loaded therein is conducted to its outer surfacewhere it can be removed by convection. In one embodiment, the canister6200 is formed of a stainless steel due to its corrosion resistantnature. In other embodiments, the canister 6200 can be formed of othermetals or metal alloys. Suitable canisters include multi-purposecanisters (“MPCs”) and, in certain instances, can include thermallyconductive casks that are hermetically sealed for the dry storage ofhigh level radioactive waste. Typically, such canisters comprise ahoneycomb basket, or other structure, positioned therein to accommodatea plurality of SNF rods in spaced relation. In one embodiment, thecanister 6200 is an MPC that is configured to achieve an internalnatural cyclical thermosiphon flow within the internal volume of thecanister 6200. An example of one such MPC is disclosed in U.S. Pat. No.5,898,747, issued to Singh on Apr. 27, 1999, the entirety of which ishereby incorporated by reference. Another MPC that is particularlysuited for use in the ventilated storage system 61000 is disclosed inU.S. Pat. No. 8,135,107, issued to Singh et al. on Mar. 13, 2012, theentirety of which is hereby incorporated by reference.

The ventilated cask 6600 is designed to accept the canister 6200. Theventilated cask 6600, in the exemplified embodiment, is in the style ofa ventilated vertical overpack (“VVO”) and comprises a cask body 6601and a cask lid 6602. However, in other embodiments, the ventilated cask6600 can take on a wide variety of structures, including any type ofstructure that is used to house the canister and provide adequateradiation shielding for the SNF loaded within the canister.

The ventilated cask 6600 generally comprises a cask body 6601 and a casklid 6602 positioned atop the cask body 6601. The cask body 6601comprises an outer surface 6603 and an inner surface 6604 that forms astorage cavity 6605 for receiving high level radioactive waste, which isin the exemplified embodiment is contained within the canister 6200. Thecask lid is positioned atop the cask body 6601 to encloses a top end ofthe storage cavity 6605. In the exemplified embodiment, the cask body6601 comprises an inner metal shell 6606 and an outer metal shell 6607circumferentially surrounding the inner metal shell 6600 so that anannulus 6608 is formed therebetween. As discussed in greater detailbelow, the annulus 6608 is filled with concrete 6609 (or another gammaradiation absorbing material). The cask body 6601 further comprises ametal baseplate 6610 and an annular top plate 6611 that are connected tothe bottom and top edges of the inner and outer metal shells 6606, 6607respectively. In one embodiment, each of the inner metal shell 6606, theouter metal shell 6607, the metal baseplate 6610 and the annular topplate 6611 are formed of a steel, such as carbon steel or stainlesssteel.

The cask body 6600 is a rugged, heavy-walled cylindrical vessel. Themain structural function of the cask body 6600 is provided by its steelcomponents while the main radiation shielding function is provided bythe annular concrete mass 6609. The plain concrete mass 6609 between theinner and outer metal steel shells 6606, 6607 is specified to providethe necessary shielding properties (dry density) and compressivestrength for the ventilated storage system 61000. The principal functionof the concrete mass 6609 is to provide shielding against gamma andneutron radiation.

The cask body 6602 extends along a longitudinal axis A-A from a bottomend 6614 to a top end 6615. In the exemplified embodiment, thelongitudinal axis A-A is vertically oriented. The cask body has avertical height V_(B) measured from the bottom end 6614 to the top end6615. The storage cavity 6605, in the exemplified embodiment, has atransverse cross-sectional that accommodates no more than one of thecanister 6200. When the canister 6200 containing high level radioactivewaste is positioned within the storage cavity 6605, an annular gap 6616exists between an outer surface 6201 of the canister 6200 and the innersurface 6604 of the cask body 6601. As will be discussed in greaterdetail below, the annular gap 6616 forms a vertical annular passagewayfrom the plurality of the inlet ducts to the outlet ducts so thatnatural convective cooling of the canister 6200 can be achieved.

The cask lid 6602 is a weldment of steel plates 6612 filled with a plainconcrete mass 6613 that provides neutron and gamma attenuation tominimize skyshine. The cask lid 6602 is removably secured to the top end6615 of the cask body 6601. When secured to the cask body 6601, surfacecontact between the cask lid 6602 and the cask body 6601 forms alid-to-body interface. The cask lid 6601 is preferably non-fixedlysecured to the cask body 6601 and encloses the top end of the storagecavity 6610 formed by the cask body 6601.

The ventilated cask 6600 further comprises a plurality of outlet ducts6617 extending from a top 6618 of the storage cavity 6605 to an ambientatmosphere 6700. In the exemplified embodiment, the plurality of outletducts 6617 are formed in the cask lid 6602. However, in alternateembodiments, the plurality of outlet ducts 6617 can be formed in thecask body 6601. The plurality of outlet ducts 6617 allow heated air thatrises within the annular gap 6616 and gather within the top 6618 of thestorage cavity 6605 to exit the ventilates cask 6600.

The ventilated cask 6600 further comprises a plurality of inlet ducts6619A-D. Each of the inlet ducts 6619A-D extend from a first opening6620A-D in the outer surface 6603 of the cask body 6601 to a secondopening 6621A-D in the inner surface 6604 of the cask body 6601. In theexemplified embodiment, the plurality of inlet ducts 6619A-D comprise anuppermost set of inlet ducts 6619A, a first middle set of inlet ducts6619B, a second middle set of inlet ducts 6619C, and a lowermost set ofinlet ducts 6619B. In certain other embodiments, more or less sets ofinlet ducts can be used as desired. As shown in FIG. 64, the secondopenings 6621D of the lowermost set of air inlet ducts 6619D are locatedat a first vertical distance V₁ from the bottom end 6614 of the caskbody 6601. The second openings 6621A of the uppermost set of air inletducts 6619A are located at a second vertical distance V₂ from the bottomend 6614 of the cask body 6601. The second openings 6621C of the firstmiddle set of inlet ducts 6619C are at a third vertical distance V₃ fromthe bottom end 6614 of the cask body 6601. The second openings 6621B ofthe second middle set of inlet ducts 6619B are at a fourth verticaldistance V₄ from the bottom end 6614 of the cask body 6601. The secondvertical distance V₂ is greater than the first vertical distance V₁. Thethird vertical distance V₃ is greater than the first vertical distanceV₁ and less than the second vertical distance V₂. The fourth verticaldistance V₄ is greater than the third vertical distance V₃ and less thanthe second vertical distance V₂. In certain embodiments, the secondvertical height V₂ is equal to or less than 50% of the vertical heightV_(B) of the cask body 6601. In another embodiment, the second height V₂is greater than or equal to 20% of the vertical height V_(B) of the caskbody 6601. In still another embodiment, the second vertical height V₂ isin a range of 20% to 50% of the vertical height V_(B) of the cask body6601.

The plurality of inlet ducts 6619A-D are metal tubes that are locatedwithin the annulus 6608 and extend between the first openings 6620A-D,which are formed in the outer metal shell 6607, and the second openings6621A-D, which are formed in the inner metal shell 6606. The remainingvolume of the annulus 6608 is filled with concrete and, thus, theplurality of inlet ducts 6619A-D are embedded in the concrete 6609.

Each of the plurality of inlet ducts 6619A-D forms a tortuous paththrough the cask body 6601 such that a line of sight does not exist fromthe storage cavity 6605 to outside 6700 of the cask body 6601. Thus,radiation cannot escape through the inlet ducts 6619A-D despite being atthe same height as the canister 6200. As can best be seen in FIG. 65,each of the plurality of inlet vents 6619A-D is independent and distinctfrom all other ones of the plurality of inlet vents 6619A-D along theentire length thereof.

The second openings 6621A-D of all of the sets of inlet ducts 6619A-Dare circumferentially arranged about the longitudinal axis A-A of thecask body 6601 (which is also the longitudinal axis A-A of the storagecavity 6605) in an equi-spaced symmetric manner. Moreover, in theexemplified embodiment, the second openings 6621A-D of all of the setsof inlet ducts 6619A-D are also in vertical alignment each other incolumns. In other embodiments, the second openings 6621A-D of all of thesets of inlet ducts 6619A-D can be vertically offset from set to set. Inone embodiment, each of the sets of inlet ducts 6619A-D comprises atleast six of the inlet ducts. In another embodiment, each of the sets ofinlet ducts 6619A-D comprises at least eight of the inlet ducts. Inother embodiments, each of the sets of inlet ducts 6619A-D may includemore or less inlet ducts. Moreover, in one embodiment, the number ofinlet ducts may vary between the sets of inlet ducts 6619A-D.

The lowermost set of inlet ducts 6619D collectively have a firsteffective cross-sectional area. The uppermost set of inlet ducts 6619Acollectively have a second effective cross-sectional area. In oneembodiment, the second effective cross-sectional area is greater thanthe first effective cross-sectional area. In other embodiments, thefirst middle set of inlet ducts 6619C collectively have a thirdeffective cross-sectional area while the second middle set of inletducts 6619B collectively have a fourth effective cross-sectional area.In one embodiment, each of the third and fourth effectivecross-sectional areas is greater than the first effectivecross-sectional area. In another embodiment, each of the second, thirdand fourth effective cross-sectional areas are substantially equal toone another and greater than the first effective cross-sectional area

The second openings 6621A-D of the plurality of inlet ducts 6619A-D arearranged in a pattern on the inner surface 6604 of the cask body 6601.As will be described in greater detail below, this pattern and thesecond vertical distance V₂ are selected to maintain more than 90% ofthe vertical height V_(C) of the metal canister above a predeterminedthreshold temperature at a predetermined heat generation rate of thehigh level radioactive waste stored therein. The vertical height V_(C)of the canister 6200 is measured from a bottom end 6202 of the canister6200 to a top end 6203 of the canister 6200.

In the exemplified embodiment, the second openings 6621A-D are arrangedin a pattern of horizontally aligned rows and vertically alignedcolumns. In certain other embodiments, however, the second openings6621A-D are arranged in a pattern that does not include distinct sets ofthe second openings 6621A-D (or sets of the inlet ducts 6619A-D). In onesuch pattern, the second openings 6621A-D are arranged in a horizontallyand vertically staggered manner.

The cask body 6601, in certain embodiments, can be conceptually dividedinto a lower axial section AL and an upper axial section AU. The loweraxial section AL is defined from the bottom end 6614 of the cask body6601 to the vertical height of an uppermost one of the second openings6621A-D of the plurality of air inlet ducts 6619A-D. Thus, all of thesecond openings 6621A-D of the plurality of air inlet ducts 6619A-D willbe located in the lower axial section AL. The upper axial section AU isdefined from the top end 6615 of the cask body 6601 to the verticalheight of the uppermost one of the second openings 6621A-D of theplurality air inlet ducts 6619A-D. Thus, the upper axial section AU isfree of the second openings 6621A-D of the plurality of air inlet ducts6619A-D.

In such an embodiment, the pattern of the second openings 6621A-D isconfigured and the vertical height of the uppermost one of the secondopenings 6621A-D is selected to maintain more than 90% of a verticalheight of the metal canister 6200 above a predetermined thresholdtemperature for a predetermined heat generation rate of the high levelradioactive waste. In another embodiment, the pattern of the secondopenings 6621A-D is configured and the vertical height of the uppermostone of the second openings 6621A-D is selected to maintain more than 95%of the vertical height of the metal canister 6200 above thepredetermined threshold temperature for the predetermined heatgeneration rate of the high level radioactive waste. In even anotherembodiment, the pattern of the second openings 6621A-D is configured andthe vertical height of the uppermost one of the second openings 6621A-Dis selected to maintain more than 97% of the vertical height of themetal canister 6200 above the predetermined threshold temperature forthe predetermined heat generation rate of the high level radioactivewaste.

In one embodiment, the predetermined threshold temperature is the sum ofan ambient air temperature outside of the ventilated cask 6600 and apositive temperature value. In one embodiment, the positive temperaturevalue is equal to or greater than about 90 degrees Celsius to preventSCC.

The ventilated system 61000 can further comprises a plurality of plugsdetachably coupled to the cask to body 6601 to seal the plurality ofinlet ducts 6619A-D to accommodate for decay of the heat generation rateof the high level radioactive waste.

As set forth above, the cask body 6601 comprises a large number of smallcircumferentially and vertically distributed inlet ducts 6619-A-D. Theinlet ducts 6619A-D are sufficiently small and curved so that they don'tpermit radiation streaming. The inlet ducts 6619A-D are located in thebottom half of the cask body 6601 while the outlet duct(s) 6617 is/arelocated in the top region as of the ventilated cask 6600. The newconfiguration of the inlet ducts 6619A-D reduces the air flow in thebottom region of the storage cavity 6605, causing the metal surfacetemperature of the canister 6200 to become elevated. In addition, airisolator channels (AICs) can be used to shield the weld seams of thecanister 6200 and the adjacent heat affected zones from the coolingaction of flowing ventilation air. The AICs can be made of spring steelconnected to the cask body 6601. The combined effect of the AICs and thedistributed air inlets 6619-A-D is to elevate the surface temperature ofthe most SCC prone portions of the canister 6200 out of the vulnerablerange (“the V-zone”).

Finally, as the heat emission rate in the high level radioactive wastewithin the canister 6200 decreases, the small inlet ducts 6619A-D can becapped/sealed so that the canister surface 6201 temperature ismaintained above the V-zone (i.e., above the predetermined thresholdtemperature). In cold conditions and after many years of decay, it isentirely conceivable that all inlet vents 6619A-B are capped, and eventhe outlet vent(s) 6617 are capped. After the need for ventilation nolonger exists, it may be prudent to fill the annulus gap 6616 with inertgas (say, nitrogen) to permanently banish the specter of SCC andhermetically seal the storage cavity 6605.

To evaluate effectiveness of the enhanced design, the cask body 6601 ismodified for a representative case wherein the bottom ducts area isdistributed to inlet ducts placed at four elevations 0 ft, 4.8 ft, 6.8ft and 8.8 ft in the ratio of 1:3:3:3. The modified cask body 6601 isanalyzed using the FLUENT axisymmetric model at the same conditions asthe prior art ventilated system of FIG. 60 (28.74 kW heat load and 26.6deg. C. ambient temperature). The canister axial temperature profile isshown in FIG. 65 for the ventilation system 61000 of the presentinvention with the profile for the prior art ventilated system 1superimposed for comparison purpose. The results show the following: (1)the present invention works as intended by raising the temperature ofthe cold bottom end of the canister substantially; (2) the distributeddesign of the inlets 6619A-D greatly diminishes the SCC prone length(the affected length is reduced from 10.4% to 2.4%); and (3) the maximumshell temperatures reached in the upper region of the canister 6200 areessentially identical (this provides reasonable assurance that fueltemperatures inside the canister 200 are not affected by the distributeddesign of the inlets ducts 6619A-D).

When the canister 6200 is loaded with SNF and positioned within thestorage cavity 6605, heat generated by the SNF within the canister 6200conducts to the outer surface 6201 of the canister 6200. This heat thenwarms the air located within the annular gap 6616. As a result of beingheated, this warmed air rises within the annular gap 6616 and eventuallyexits the ventilated cask 6600 via the outlet ducts 6617 as heated air.Due to a thermosiphon effect created by the exiting heated air, cool airis drawn into the inlet ducts 6619A-D. This cool air flows through theinlet ducts 6619A-D and is the drawn upward into the annular gap 6616where it becomes heated and begins to rise, thereby creating acontinuous cycle, known as the chimney-effect. Thus, the heat generatedby the SNF within the canister 6200 causes a natural convective flow ofair through a ventilation passageway of the ventilated cask 6600. In theexemplified embodiment, the ventilation passageway is collectivelyformed by the inlet ducts 6619A-D, the annular gap 6616 and the outletducts 6617. In the exemplified embodiment, the ventilated cask 6600 isfree of forced cooling equipment, such as blowers and closed-loopcooling systems. The rate of air flow through the ventilation passagewayof the ventilated cask 6600 is governed, in part, by the heat generationrate of the SNF within the canister 6200 and the number of inletventilation ducts 6619A-D that are open.

In accordance with a method of the present invention, the metal canister6200 containing high level radioactive waste having a heat generationrate is positioned in the storage cavity 6605. The cask lid 6602 ispositioned atop the cask body 6601. As time passes, the heat generationrate of the high level radioactive waste decreases. Thus, in order tokeep the outer surface 6201 of the canister above the desired SCCthreshold, selected ones of the plurality of inlet ducts 6619A-B aresealed over time as a function of the decay of the heat generation rateto maintain a predetermined percentage of a vertical height of the metalcanister 6200 above a predetermined threshold temperature. Sealing ofselected ones of the plurality of inlet ducts 6619A-B reduces thenatural convective flow rate of air through the storage cavity 6605. Inone embodiment, a first set of the plurality of inlet ducts are sealedat a first point in time. In one example, the first set of the pluralityof inlet ducts can be the lowermost ventilation ducts 6619D. As the heatgeneration rate of the high level radioactive waste continues todecrease, it will become necessary to further reduce the convective airflow through the ventilated cask 6600. Thus, at a second later point intime, a second set of the plurality of inlet ducts are sealed, which canbe the second middle set of inlet ducts 6619C. In one embodiment,sealing of the inlet ducts continues and the inlet ducts 6619A-D aresealed in sets moving upward from the bottom end 6614 as time passes

According to the present invention, it can be seen that utilizing aplurality of inlet vents 6619A-D that are decreased in size and spreadout (as compared to prior art ventilated cask 1) so as to introduce coolair into the storage cavity 6605 over an increased height of thecanister 6200 results in an increased portion of the outer surface 6201of the canister 6200 remaining above the SCC threshold temperature foran increased period of time. Thus, the dangers associated with SCC areminimized.

As used throughout, ranges are used as shorthand for describing each andevery value that is within the range. Any value within the range can beselected as the terminus of the range. In addition, all references citedherein are hereby incorporated by referenced in their entireties. In theevent of a conflict in a definition in the present disclosure and thatof a cited reference, the present disclosure controls.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques. It is tobe understood that other embodiments may be utilized and structural andfunctional modifications may be made without departing from the scope ofthe present invention. Thus, the spirit and scope of the inventionshould be construed broadly as set forth in the appended claims.

1.-217. (canceled)
 218. A method of forming a sealed canister, themethod comprising placing a top plate on a top opening of a side wall, abottom of the side wall being sealed to a base plate, wherein the topplate includes a top surface with a top edge having a bevel and with achannel set in from the top edge; and forming a weld between the beveledtop edge and the top opening of the side wall to seal the top plate tothe side wall.
 219. The method of claim 218, further comprising: placinga first probe in the channel and a second probe opposite the first probeand adjacent the side wall, such that the weld is disposed between thetwo probes; activating the first and second probes to determine anintegrity of a volume of the weld between the probes; and moving thefirst and second probes synchronously around the top plate to determinethe integrity of an entire volume of the weld.
 220. The method of claim218, wherein the base plate, side wall, and top plate form ahermetically sealed vessel.
 221. The method of claim 218, wherein thecircumferential channel is approximately as deep as the bevel extendsbelow the top surface.
 222. The method of claim 218, wherein thecircumferential channel is deeper than the bevel extends below the topsurface.
 223. The method of claim 218, wherein the bevel is formed asone of a J-cut or a half V-cut.
 224. The method of claim 218, whereinthe first and second probes comprise ultrasound probes.
 225. A method ofstoring radioactive materials, the method comprising: placingradioactive materials in a cavity formed by a side wall having a bottomsealed to a base plate; placing a top plate on a top opening of the sidewall, the top plate including a top surface with a top edge having abevel and with a channel set in from the top edge; forming a weldbetween the beveled top edge and the top opening of the side wall toseal the top plate to the side wall, so that the cavity is sealed;placing a first probe in the channel and a second probe opposite thefirst probe and adjacent the side wall, such that the weld is disposedbetween the two probes; activating the first and second probes todetermine an integrity of a volume of the weld between the probes; andmoving the first and second probes synchronously around the top plate todetermine the integrity of an entire volume of the weld.
 226. The methodof claim 225, wherein the circumferential channel is approximately asdeep as the bevel extends below the top surface.
 227. The method ofclaim 225, wherein the circumferential channel is deeper than the bevelextends below the top surface.
 228. The method of claim 225, wherein thebevel is formed as one of a J-cut or a half V-cut.
 229. The method ofclaim 225, wherein the cavity is hermetically by the formed weld.